I'm collecting temperature data at ten minute intervals and plotting the last three days. Currently, I'm using xrange to limit the range of the plot. Is this the right way to do this? I'm concerned that gnuplot is internally creating a plot for all the data in the file and just showing what's in range. That could start to be a problem when I have months of data.
Here's the gnuplot code:
#!/opt/local/bin/gnuplot
# Make PNG for iPhone
set terminal pngcairo enhanced background "#000000" font "Lato-Light,20" linewidth 1 rounded size 1366,660
set output "/Users/steve/Documents/Temperature History/temperatureHistory.png"
dataFileHistory = "/Users/steve/Documents/Temperature History/Temperature History.csv"
set datafile separator ','
set xdata time
# create function to ignore first four characters of time string
# http://stackoverflow.com/questions/26793373/how-to-ignore-timezone-in-csv-data
timefmt = "%b %d %H:%M:%S %Y"
timeval(s) = strptime(timefmt, substr(s, 5, strlen(s)))
set border linetype rgb "#666666"
set boxwidth 0.25 relative
set key off
#set style fill transparent solid 1
set style fill solid 1
set style line 1 linetype rgb "#666666" lw 2 #outside
set style line 2 linetype rgb "#990099" lw 3 #bedroom
set style line 3 linetype rgb "#999900" #upstairs
set style line 4 linetype rgb "#0055DD" #downstairs
set style line 5 linetype rgb "#666666" #grid
# X Axis
endTime = time(0) - 7*60*60  #Adjust for time zone
startTime = endTime-72*60*60
set xtics 6*60*60 format "%l %p" nomirror
set xrange [startTime:endTime]
# Y Axis
set ytics format "%2.0f°" nomirror
set grid ytics linestyle 5
plot dataFileHistory using (timeval(strcol(1))):2 with lines linestyle 1, \
    dataFileHistory using (timeval(strcol(1))):3 with lines linestyle 2, \
    dataFileHistory using (timeval(strcol(1))):4 with lines linestyle 3, \
    dataFileHistory using (timeval(strcol(1))):5 with lines linestyle 4
# Make PNG for iPad
set terminal pngcairo enhanced background "#000000" font "Lato-Light,20" linewidth 1 rounded size 2048,689
set output "/Users/steve/Documents/Temperature History/temperatureHistory-iPad.png"
plot dataFileHistory using (timeval(strcol(1))):2 with lines linestyle 1, \
    dataFileHistory using (timeval(strcol(1))):3 with lines linestyle 2, \
    dataFileHistory using (timeval(strcol(1))):4 with lines linestyle 3, \
    dataFileHistory using (timeval(strcol(1))):5 with lines linestyle 4
Here's a sample of the data:
Fri Jul  3 10:20:01 2015, 75.1, 80.0, 80.0, 75.0
Fri Jul  3 10:30:01 2015, 76.1, 80.0, 80.0, 75.0
Fri Jul  3 10:40:01 2015, 77.3, 80.0, 80.0, 75.0
Fri Jul  3 10:50:01 2015, 78.5, 80.0, 80.0, 75.0
Fri Jul  3 11:00:01 2015, 79.5, 80.0, 80.0, 75.0
Fri Jul  3 11:10:01 2015, 80.2, 80.0, 80.0, 75.0
Fri Jul  3 11:20:02 2015, 80.6, 80.0, 80.0, 75.0
Fri Jul  3 11:30:01 2015, 80.6, 80.0, 80.0, 75.0
Fri Jul  3 11:40:01 2015, 81.5, 81.0, 80.0, 75.0
Fri Jul  3 11:50:01 2015, 81.2, 81.0, 80.0, 75.0
Fri Jul  3 12:00:01 2015, 82.2, 81.0, 80.0, 75.0
Fri Jul  3 12:10:00 2015, 83.3, 81.0, 81.0, 75.0
Fri Jul  3 12:20:00 2015, 83.1, 81.0, 81.0, 75.0
Fri Jul  3 12:30:00 2015, 82.9, 81.0, 81.0, 75.0
Fri Jul  3 12:40:00 2015, 83.4, 81.0, 81.0, 75.0
Fri Jul  3 12:50:00 2015, 84.2, 81.0, 81.0, 75.0
Fri Jul  3 13:00:01 2015, 84.6, 81.0, 81.0, 75.0
Fri Jul  3 13:10:00 2015, 85.4, 81.0, 82.0, 75.0
Fri Jul  3 13:20:00 2015, 86.5, 81.0, 82.0, 75.0
Fri Jul  3 13:30:00 2015, 87.5, 81.0, 82.0, 75.0
Fri Jul  3 13:40:00 2015, 89.7, 81.0, 82.0, 75.0
Fri Jul  3 13:50:00 2015, 90.5, 81.0, 82.0, 75.0
Fri Jul  3 14:00:01 2015, 91.3, 81.0, 82.0, 75.0
Fri Jul  3 14:10:01 2015, 91.9, 82.0, 83.0, 75.0
Fri Jul  3 14:20:01 2015, 92.8, 82.0, 83.0, 75.0
Fri Jul  3 14:30:01 2015, 93.5, 82.0, 83.0, 75.0
Fri Jul  3 14:40:01 2015, 93.8, 82.0, 83.0, 75.0
Fri Jul  3 14:50:01 2015, 93.6, 82.0, 83.0, 75.0
Fri Jul  3 15:00:01 2015, 94.2, 83.0, 84.0, 75.0
Fri Jul  3 15:10:01 2015, 94.5, 83.0, 84.0, 75.0
Fri Jul  3 15:20:01 2015, 94.6, 83.0, 84.0, 75.0
Fri Jul  3 15:30:01 2015, 94.6, 83.0, 84.0, 75.0
Fri Jul  3 15:40:01 2015, 94.0, 83.0, 84.0, 75.0
Fri Jul  3 15:50:01 2015, 93.3, 83.0, 84.0, 75.0
Fri Jul  3 16:00:01 2015, 92.9, 83.0, 85.0, 75.0
Fri Jul  3 16:10:01 2015, 92.6, 83.0, 85.0, 75.0
Fri Jul  3 16:20:01 2015, 92.5, 83.0, 85.0, 75.0
Fri Jul  3 16:30:01 2015, 92.0, 83.0, 85.0, 75.0
Fri Jul  3 16:40:01 2015, 91.7, 83.0, 85.0, 75.0
Fri Jul  3 16:50:01 2015, 91.2, 83.0, 85.0, 75.0
Fri Jul  3 17:00:01 2015, 89.9, 84.0, 85.0, 75.0
Fri Jul  3 17:10:01 2015, 89.6, 84.0, 85.0, 75.0
Fri Jul  3 17:20:01 2015, 89.0, 84.0, 85.0, 75.0
Fri Jul  3 17:30:01 2015, 88.8, 84.0, 85.0, 75.0
Fri Jul  3 17:40:01 2015, 87.8, 84.0, 85.0, 75.0
Fri Jul  3 17:50:01 2015, 87.6, 84.0, 85.0, 75.0
Fri Jul  3 18:00:01 2015, 86.9, 84.0, 85.0, 75.0
Fri Jul  3 18:10:01 2015, 86.7, 84.0, 85.0, 75.0
Fri Jul  3 18:20:01 2015, 86.1, 84.0, 85.0, 75.0
Fri Jul  3 18:30:01 2015, 85.7, 84.0, 85.0, 75.0
Fri Jul  3 18:40:01 2015, 85.5, 84.0, 85.0, 75.0
Fri Jul  3 18:50:01 2015, 85.1, 84.0, 85.0, 75.0
Fri Jul  3 19:00:01 2015, 84.4, 84.0, 85.0, 75.0
Fri Jul  3 19:10:01 2015, 84.2, 85.0, 85.0, 76.0
Fri Jul  3 19:20:01 2015, 83.8, 85.0, 85.0, 76.0
Fri Jul  3 19:30:01 2015, 83.4, 85.0, 85.0, 76.0
Fri Jul  3 19:40:01 2015, 82.4, 85.0, 85.0, 76.0
Fri Jul  3 19:50:01 2015, 82.2, 85.0, 85.0, 76.0
Fri Jul  3 20:00:01 2015, 81.8, 85.0, 85.0, 76.0
Fri Jul  3 20:10:01 2015, 81.3, 85.0, 85.0, 76.0
Fri Jul  3 20:20:01 2015, 80.2, 85.0, 85.0, 76.0
Fri Jul  3 20:30:01 2015, 79.7, 85.0, 85.0, 76.0
Fri Jul  3 20:40:01 2015, 79.1, 85.0, 85.0, 76.0
Fri Jul  3 20:50:01 2015, 78.8, 85.0, 85.0, 76.0
Fri Jul  3 21:00:01 2015, 77.9, 85.0, 85.0, 76.0
Fri Jul  3 21:10:01 2015, 77.3, 85.0, 85.0, 76.0
Fri Jul  3 21:20:01 2015, 77.0, 85.0, 85.0, 76.0
Fri Jul  3 21:30:01 2015, 76.4, 85.0, 85.0, 76.0
Fri Jul  3 21:40:01 2015, 75.9, 85.0, 84.0, 76.0
Fri Jul  3 21:50:01 2015, 75.5, 85.0, 84.0, 76.0
Fri Jul  3 22:00:01 2015, 75.3, 85.0, 84.0, 76.0
Fri Jul  3 22:10:01 2015, 74.9, 85.0, 84.0, 76.0
Fri Jul  3 22:20:01 2015, 74.3, 85.0, 84.0, 76.0
Fri Jul  3 22:30:01 2015, 74.0, 85.0, 84.0, 76.0
Fri Jul  3 22:40:01 2015, 73.5, 84.0, 84.0, 76.0
Fri Jul  3 22:50:01 2015, 73.3, 84.0, 84.0, 76.0
Fri Jul  3 23:00:01 2015, 73.1, 84.0, 84.0, 76.0
Fri Jul  3 23:10:01 2015, 72.7, 84.0, 84.0, 76.0
Fri Jul  3 23:20:01 2015, 72.4, 84.0, 84.0, 76.0
Fri Jul  3 23:30:01 2015, 72.2, 84.0, 84.0, 76.0
Fri Jul  3 23:40:00 2015, 71.9, 84.0, 83.0, 76.0
Fri Jul  3 23:50:00 2015, 71.4, 84.0, 83.0, 76.0
Sat Jul  4 00:00:01 2015, 71.2, 84.0, 83.0, 76.0
Sat Jul  4 00:10:00 2015, 71.0, 84.0, 83.0, 76.0
Sat Jul  4 00:20:00 2015, 70.4, 84.0, 83.0, 76.0
Sat Jul  4 00:30:00 2015, 70.1, 84.0, 83.0, 76.0
Sat Jul  4 00:40:00 2015, 69.9, 84.0, 82.0, 76.0
Sat Jul  4 00:50:00 2015, 69.7, 84.0, 82.0, 76.0
Sat Jul  4 01:00:00 2015, 69.6, 84.0, 82.0, 76.0
Sat Jul  4 01:10:01 2015, 69.3, 84.0, 82.0, 76.0
Sat Jul  4 01:20:00 2015, 69.1, 84.0, 82.0, 76.0
Sat Jul  4 01:30:01 2015, 68.9, 84.0, 82.0, 76.0
Sat Jul  4 01:40:01 2015, 68.8, 84.0, 81.0, 76.0
Sat Jul  4 01:50:01 2015, 68.5, 84.0, 81.0, 76.0
Sat Jul  4 02:00:00 2015, 68.4, 84.0, 81.0, 76.0
Sat Jul  4 02:10:00 2015, 68.3, 83.0, 81.0, 76.0
Sat Jul  4 02:20:00 2015, 68.2, 83.0, 81.0, 76.0
Sat Jul  4 02:30:00 2015, 67.9, 83.0, 81.0, 76.0
Sat Jul  4 02:40:00 2015, 67.9, 83.0, 81.0, 76.0
Sat Jul  4 02:50:01 2015, 67.9, 83.0, 81.0, 76.0
Sat Jul  4 03:00:01 2015, 67.7, 83.0, 81.0, 76.0
Sat Jul  4 03:10:00 2015, 67.6, 83.0, 81.0, 76.0
Sat Jul  4 03:20:00 2015, 67.6, 83.0, 81.0, 76.0
Sat Jul  4 03:30:01 2015, 67.4, 83.0, 81.0, 76.0
Sat Jul  4 03:40:01 2015, 67.1, 83.0, 80.0, 75.0
Sat Jul  4 03:50:01 2015, 67.0, 83.0, 80.0, 75.0
Sat Jul  4 04:00:00 2015, 66.8, 83.0, 80.0, 75.0
Sat Jul  4 04:10:00 2015, 66.7, 83.0, 80.0, 75.0
Sat Jul  4 04:20:00 2015, 66.4, 83.0, 80.0, 75.0
Sat Jul  4 04:30:01 2015, 66.3, 83.0, 80.0, 75.0
Sat Jul  4 04:40:01 2015, 66.5, 83.0, 80.0, 75.0
Sat Jul  4 04:50:01 2015, 66.2, 83.0, 80.0, 75.0
Sat Jul  4 05:00:00 2015, 65.9, 83.0, 80.0, 75.0
Sat Jul  4 05:10:00 2015, 65.9, 82.0, 80.0, 75.0
Sat Jul  4 05:20:00 2015, 65.8, 82.0, 80.0, 75.0
Sat Jul  4 05:30:01 2015, 65.9, 82.0, 80.0, 75.0
Sat Jul  4 05:40:01 2015, 65.5, 82.0, 79.0, 75.0
Sat Jul  4 05:50:01 2015, 65.5, 82.0, 79.0, 75.0
Sat Jul  4 06:00:00 2015, 65.4, 82.0, 79.0, 75.0
Sat Jul  4 06:10:00 2015, 65.3, 82.0, 79.0, 75.0
Sat Jul  4 06:20:00 2015, 65.0, 82.0, 79.0, 75.0
Sat Jul  4 06:30:00 2015, 65.1, 82.0, 79.0, 75.0
Sat Jul  4 06:40:00 2015, 64.9, 82.0, 79.0, 75.0
Sat Jul  4 06:50:01 2015, 65.2, 82.0, 79.0, 75.0
Sat Jul  4 07:00:00 2015, 65.3, 82.0, 79.0, 75.0
Sat Jul  4 07:10:00 2015, 65.3, 82.0, 79.0, 75.0
Sat Jul  4 07:20:00 2015, 65.4, 82.0, 79.0, 75.0
Sat Jul  4 07:30:00 2015, 65.7, 82.0, 79.0, 75.0
Sat Jul  4 07:40:00 2015, 65.9, 82.0, 79.0, 75.0
Sat Jul  4 07:50:01 2015, 66.3, 82.0, 79.0, 75.0
Sat Jul  4 08:00:01 2015, 66.6, 82.0, 79.0, 75.0
Sat Jul  4 08:10:01 2015, 66.9, 81.0, 79.0, 75.0
Sat Jul  4 08:20:00 2015, 67.1, 81.0, 79.0, 75.0
Sat Jul  4 08:30:00 2015, 67.2, 81.0, 79.0, 75.0
Sat Jul  4 08:40:01 2015, 67.6, 81.0, 79.0, 75.0
Sat Jul  4 08:50:01 2015, 67.8, 81.0, 79.0, 75.0
Sat Jul  4 09:00:00 2015, 68.5, 81.0, 79.0, 75.0
Sat Jul  4 09:10:00 2015, 68.8, 81.0, 79.0, 75.0
Sat Jul  4 09:20:00 2015, 69.2, 81.0, 79.0, 75.0
Sat Jul  4 09:30:00 2015, 69.9, 81.0, 79.0, 75.0
Sat Jul  4 09:40:01 2015, 71.3, 81.0, 79.0, 75.0
Sat Jul  4 09:50:00 2015, 71.9, 81.0, 79.0, 75.0
Sat Jul  4 10:00:00 2015, 72.4, 81.0, 79.0, 75.0
Sat Jul  4 10:10:00 2015, 73.0, 81.0, 79.0, 75.0
Sat Jul  4 10:20:00 2015, 74.5, 81.0, 79.0, 75.0
Sat Jul  4 10:30:00 2015, 75.6, 81.0, 79.0, 75.0
Sat Jul  4 10:40:00 2015, 76.8, 81.0, 79.0, 75.0
Sat Jul  4 10:50:00 2015, 78.2, 81.0, 79.0, 75.0
Sat Jul  4 11:00:01 2015, 80.4, 81.0, 79.0, 75.0
Sat Jul  4 11:10:00 2015, 81.7, 81.0, 80.0, 75.0
Sat Jul  4 11:20:00 2015, 83.7, 81.0, 80.0, 75.0
Sat Jul  4 11:30:00 2015, 85.6, 81.0, 80.0, 75.0
Sat Jul  4 11:40:00 2015, 86.8, 81.0, 80.0, 75.0
Sat Jul  4 11:50:00 2015, 87.1, 81.0, 80.0, 75.0
Sat Jul  4 12:00:01 2015, 87.1, 81.0, 80.0, 75.0
Sat Jul  4 12:10:00 2015, 87.8, 82.0, 80.0, 75.0
Sat Jul  4 12:20:00 2015, 87.9, 82.0, 80.0, 75.0
Sat Jul  4 12:30:00 2015, 87.4, 82.0, 80.0, 75.0
Sat Jul  4 12:40:00 2015, 87.6, 82.0, 80.0, 75.0
Sat Jul  4 12:50:00 2015, 88.0, 82.0, 81.0, 75.0
Sat Jul  4 13:00:00 2015, 89.1, 82.0, 81.0, 75.0
Sat Jul  4 13:10:03 2015, 89.3, 82.0, 81.0, 75.0
Sat Jul  4 13:20:00 2015, 89.8, 82.0, 81.0, 75.0
Sat Jul  4 13:30:00 2015, 90.9, 82.0, 81.0, 75.0
Sat Jul  4 13:40:00 2015, 92.3, 82.0, 81.0, 75.0
Sat Jul  4 13:50:00 2015, 92.6, 83.0, 82.0, 75.0
Sat Jul  4 14:00:01 2015, 93.3, 83.0, 82.0, 75.0
Sat Jul  4 14:10:01 2015, 94.3, 83.0, 82.0, 75.0
Sat Jul  4 14:20:00 2015, 94.9, 83.0, 82.0, 75.0
Sat Jul  4 14:30:00 2015, 94.2, 83.0, 82.0, 75.0
Sat Jul  4 14:40:00 2015, 94.2, 83.0, 82.0, 75.0
Sat Jul  4 14:50:00 2015, 93.9, 83.0, 82.0, 75.0
Sat Jul  4 15:00:00 2015, 92.3, 83.0, 82.0, 75.0
Sat Jul  4 15:10:01 2015, 91.8, 83.0, 82.0, 75.0
Sat Jul  4 15:20:00 2015, 91.0, 83.0, 82.0, 75.0
Sat Jul  4 15:30:00 2015, 90.5, 83.0, 82.0, 75.0
Sat Jul  4 15:40:00 2015, 89.3, 83.0, 82.0, 75.0
Sat Jul  4 15:50:00 2015, 89.1, 83.0, 82.0, 75.0
Sat Jul  4 16:00:00 2015, 88.5, 84.0, 83.0, 75.0
Sat Jul  4 16:10:00 2015, 88.0, 84.0, 83.0, 75.0
Sat Jul  4 16:20:00 2015, 87.6, 84.0, 83.0, 75.0
Sat Jul  4 16:30:00 2015, 87.4, 84.0, 83.0, 75.0
Sat Jul  4 16:40:00 2015, 87.4, 84.0, 83.0, 75.0
Sat Jul  4 16:50:00 2015, 87.5, 84.0, 83.0, 75.0
Sat Jul  4 17:00:00 2015, 87.4, 84.0, 83.0, 75.0
Sat Jul  4 17:10:00 2015, 87.4, 84.0, 83.0, 75.0
Sat Jul  4 17:20:01 2015, 87.1, 84.0, 83.0, 75.0
Sat Jul  4 17:30:00 2015, 87.2, 84.0, 83.0, 75.0
Sat Jul  4 17:40:00 2015, 86.9, 84.0, 83.0, 75.0
Sat Jul  4 17:50:00 2015, 86.6, 84.0, 83.0, 75.0
Sat Jul  4 18:00:00 2015, 86.6, 84.0, 83.0, 76.0
Sat Jul  4 18:10:00 2015, 86.3, 84.0, 83.0, 76.0
Sat Jul  4 18:20:01 2015, 86.3, 84.0, 83.0, 76.0
Sat Jul  4 18:30:00 2015, 86.0, 84.0, 83.0, 76.0
Sat Jul  4 18:40:00 2015, 85.8, 84.0, 83.0, 76.0
Sat Jul  4 18:50:00 2015, 85.6, 84.0, 83.0, 76.0
Sat Jul  4 19:00:00 2015, 85.1, 85.0, 84.0, 76.0
Sat Jul  4 19:10:00 2015, 84.8, 85.0, 84.0, 76.0
Sat Jul  4 19:20:00 2015, 84.5, 85.0, 84.0, 76.0
Sat Jul  4 19:30:01 2015, 84.1, 85.0, 84.0, 76.0
Sat Jul  4 19:40:00 2015, 83.6, 85.0, 84.0, 76.0
Sat Jul  4 19:50:00 2015, 83.1, 85.0, 84.0, 76.0
Sat Jul  4 20:00:00 2015, 82.8, 85.0, 84.0, 76.0
Sat Jul  4 20:10:00 2015, 82.2, 85.0, 84.0, 76.0
Sat Jul  4 20:20:00 2015, 81.5, 85.0, 84.0, 76.0
Sat Jul  4 20:30:01 2015, 81.2, 85.0, 84.0, 76.0
Sat Jul  4 20:40:01 2015, 80.7, 85.0, 84.0, 76.0
Sat Jul  4 20:50:00 2015, 80.1, 85.0, 84.0, 76.0
Sat Jul  4 21:00:00 2015, 79.2, 85.0, 84.0, 76.0
Sat Jul  4 21:10:00 2015, 78.7, 85.0, 84.0, 76.0
Sat Jul  4 21:20:00 2015, 78.4, 85.0, 84.0, 76.0
Sat Jul  4 21:30:01 2015, 78.0, 85.0, 84.0, 76.0
Sat Jul  4 21:40:00 2015, 77.1, 85.0, 84.0, 76.0
Sat Jul  4 21:50:00 2015, 76.7, 85.0, 84.0, 76.0
Sat Jul  4 22:00:00 2015, 76.1, 85.0, 84.0, 76.0
Sat Jul  4 22:10:00 2015, 75.8, 85.0, 84.0, 76.0
Sat Jul  4 22:20:00 2015, 75.1, 85.0, 84.0, 76.0
Sat Jul  4 22:30:02 2015, 75.0, 85.0, 84.0, 76.0
Sat Jul  4 22:40:00 2015, 74.5, 85.0, 84.0, 76.0
Sat Jul  4 22:50:00 2015, 74.3, 84.0, 83.0, 76.0
Sat Jul  4 23:00:00 2015, 73.7, 84.0, 83.0, 76.0
Sat Jul  4 23:10:01 2015, 73.4, 83.0, 82.0, 76.0
Sat Jul  4 23:20:00 2015, 73.3, 83.0, 82.0, 76.0
Sat Jul  4 23:30:00 2015, 73.0, 83.0, 82.0, 76.0
Sat Jul  4 23:40:01 2015, 72.5, 83.0, 82.0, 76.0
Sat Jul  4 23:50:00 2015, 72.2, 83.0, 81.0, 76.0
Sun Jul  5 00:00:01 2015, 71.9, 83.0, 81.0, 76.0
Sun Jul  5 00:10:00 2015, 71.7, 82.0, 82.0, 76.0
Sun Jul  5 00:20:01 2015, 71.4, 82.0, 82.0, 76.0
Sun Jul  5 00:30:00 2015, 71.2, 82.0, 82.0, 76.0
Sun Jul  5 00:40:01 2015, 71.0, 82.0, 81.0, 76.0
Sun Jul  5 00:50:00 2015, 70.7, 82.0, 81.0, 76.0
Sun Jul  5 01:00:02 2015, 70.1, 82.0, 81.0, 76.0
Sun Jul  5 01:10:01 2015, 70.0, 81.0, 80.0, 76.0
Sun Jul  5 01:20:01 2015, 69.9, 81.0, 80.0, 76.0
Sun Jul  5 01:30:01 2015, 69.7, 81.0, 80.0, 76.0
Sun Jul  5 01:40:02 2015, 69.3, 81.0, 80.0, 76.0
Sun Jul  5 01:50:01 2015, 69.2, 81.0, 80.0, 76.0
Sun Jul  5 02:00:01 2015, 69.2, 81.0, 80.0, 76.0
Sun Jul  5 02:10:00 2015, 68.8, 81.0, 80.0, 76.0
Sun Jul  5 02:20:00 2015, 68.7, 81.0, 80.0, 76.0
Sun Jul  5 02:30:01 2015, 68.6, 80.0, 80.0, 76.0
Sun Jul  5 02:40:00 2015, 68.4, 80.0, 80.0, 76.0
Sun Jul  5 02:50:02 2015, 68.1, 80.0, 80.0, 76.0
Sun Jul  5 03:00:01 2015, 67.8, 80.0, 79.0, 76.0
Sun Jul  5 03:10:01 2015, 67.7, 80.0, 79.0, 76.0
Sun Jul  5 03:20:01 2015, 67.7, 80.0, 79.0, 76.0
Sun Jul  5 03:30:00 2015, 67.6, 80.0, 79.0, 76.0
Sun Jul  5 03:40:01 2015, 67.2, 79.0, 79.0, 76.0
Sun Jul  5 03:50:01 2015, 67.4, 79.0, 79.0, 76.0
Sun Jul  5 04:00:01 2015, 66.9, 79.0, 79.0, 76.0
Sun Jul  5 04:10:01 2015, 66.8, 79.0, 78.0, 76.0
Sun Jul  5 04:20:01 2015, 66.5, 79.0, 78.0, 76.0
Sun Jul  5 04:30:01 2015, 66.6, 79.0, 78.0, 76.0
Sun Jul  5 04:40:02 2015, 66.2, 79.0, 78.0, 76.0
Sun Jul  5 04:50:01 2015, 66.4, 79.0, 78.0, 76.0
Sun Jul  5 05:00:01 2015, 65.9, 78.0, 78.0, 76.0
Sun Jul  5 05:10:02 2015, 66.1, 78.0, 78.0, 76.0
Sun Jul  5 05:20:01 2015, 65.7, 78.0, 78.0, 76.0
Sun Jul  5 05:30:01 2015, 65.6, 78.0, 78.0, 76.0
Sun Jul  5 05:40:01 2015, 65.5, 78.0, 77.0, 75.0
Sun Jul  5 05:50:01 2015, 65.4, 78.0, 78.0, 75.0
Sun Jul  5 06:00:01 2015, 65.4, 78.0, 78.0, 75.0
Sun Jul  5 06:10:01 2015, 65.1, 78.0, 77.0, 75.0
Sun Jul  5 06:20:01 2015, 65.0, 78.0, 77.0, 75.0
Sun Jul  5 06:30:01 2015, 65.1, 78.0, 77.0, 75.0
Sun Jul  5 06:40:01 2015, 65.1, 78.0, 77.0, 75.0
Sun Jul  5 06:50:01 2015, 65.1, 78.0, 77.0, 75.0
Sun Jul  5 07:00:02 2015, 65.1, 78.0, 77.0, 75.0
Sun Jul  5 07:10:01 2015, 65.3, 77.0, 77.0, 75.0
Sun Jul  5 07:20:01 2015, 65.3, 77.0, 77.0, 75.0
Sun Jul  5 07:30:01 2015, 65.2, 77.0, 77.0, 75.0
Sun Jul  5 07:40:01 2015, 65.5, 77.0, 77.0, 75.0
Sun Jul  5 07:50:01 2015, 65.7, 77.0, 77.0, 75.0
Sun Jul  5 08:00:01 2015, 65.6, 77.0, 77.0, 75.0
Sun Jul  5 08:10:01 2015, 66.0, 77.0, 77.0, 75.0
Sun Jul  5 08:20:01 2015, 66.5, 77.0, 77.0, 75.0
Sun Jul  5 08:30:01 2015, 66.8, 77.0, 77.0, 75.0
Sun Jul  5 08:40:01 2015, 67.2, 77.0, 77.0, 75.0
Sun Jul  5 08:50:01 2015, 67.6, 77.0, 77.0, 75.0
Sun Jul  5 09:00:02 2015, 68.8, 77.0, 77.0, 75.0
Sun Jul  5 09:10:01 2015, 69.4, 77.0, 77.0, 75.0
Sun Jul  5 09:20:01 2015, 69.8, 77.0, 77.0, 75.0
Sun Jul  5 09:30:02 2015, 70.7, 77.0, 77.0, 75.0
Sun Jul  5 09:40:01 2015, 72.0, 77.0, 77.0, 75.0
Sun Jul  5 09:50:01 2015, 72.7, 77.0, 77.0, 75.0
Sun Jul  5 10:00:01 2015, 73.0, 78.0, 78.0, 75.0
Sun Jul  5 10:10:01 2015, 73.7, 78.0, 78.0, 75.0
Sun Jul  5 10:20:01 2015, 74.9, 78.0, 79.0, 75.0
Sun Jul  5 10:30:01 2015, 76.4, 78.0, 79.0, 75.0
Sun Jul  5 10:40:01 2015, 77.8, 78.0, 79.0, 75.0
Sun Jul  5 10:50:01 2015, 79.3, 78.0, 79.0, 75.0
Sun Jul  5 11:00:01 2015, 81.1, 79.0, 80.0, 75.0
Sun Jul  5 11:10:01 2015, 82.4, 79.0, 80.0, 75.0
Sun Jul  5 11:20:01 2015, 84.6, 79.0, 80.0, 75.0
Sun Jul  5 11:30:01 2015, 86.2, 79.0, 80.0, 75.0
Sun Jul  5 11:40:01 2015, 89.0, 79.0, 80.0, 75.0
Sun Jul  5 11:50:01 2015, 89.7, 79.0, 80.0, 75.0
Sun Jul  5 12:00:01 2015, 89.9, 79.0, 80.0, 75.0
Sun Jul  5 12:10:01 2015, 90.1, 80.0, 82.0, 75.0
Sun Jul  5 12:20:01 2015, 90.2, 81.0, 82.0, 75.0
Sun Jul  5 12:30:02 2015, 90.0, 81.0, 82.0, 75.0
Sun Jul  5 12:40:01 2015, 89.9, 81.0, 82.0, 75.0
Sun Jul  5 12:50:01 2015, 89.9, 81.0, 83.0, 75.0
Sun Jul  5 13:00:01 2015, 90.3, 81.0, 83.0, 75.0
Sun Jul  5 13:10:02 2015, 90.9, 81.0, 83.0, 75.0
Sun Jul  5 13:20:00 2015, 91.2, 81.0, 83.0, 75.0
Sun Jul  5 13:30:01 2015, 92.1, 81.0, 83.0, 75.0
Sun Jul  5 13:40:00 2015, 93.3, 82.0, 84.0, 75.0
Sun Jul  5 13:50:00 2015, 93.8, 82.0, 84.0, 75.0
Sun Jul  5 14:00:00 2015, 94.3, 82.0, 84.0, 75.0
Sun Jul  5 14:10:00 2015, 94.9, 82.0, 85.0, 75.0
Sun Jul  5 14:20:00 2015, 96.1, 82.0, 85.0, 75.0
Sun Jul  5 14:30:00 2015, 96.0, 82.0, 85.0, 75.0
Sun Jul  5 14:40:01 2015, 96.0, 83.0, 85.0, 75.0
Sun Jul  5 14:50:00 2015, 96.3, 83.0, 85.0, 75.0
Sun Jul  5 15:00:00 2015, 96.7, 83.0, 85.0, 75.0
Sun Jul  5 15:10:00 2015, 96.5, 83.0, 86.0, 75.0
Sun Jul  5 15:20:01 2015, 96.8, 83.0, 86.0, 75.0
Sun Jul  5 15:30:00 2015, 96.7, 83.0, 86.0, 75.0
Sun Jul  5 15:40:00 2015, 95.6, 84.0, 86.0, 75.0
Sun Jul  5 15:50:00 2015, 94.9, 84.0, 86.0, 75.0
Sun Jul  5 16:00:00 2015, 94.4, 84.0, 86.0, 75.0
Sun Jul  5 16:10:00 2015, 94.1, 84.0, 86.0, 75.0
Sun Jul  5 16:20:00 2015, 93.4, 84.0, 86.0, 75.0
Sun Jul  5 16:30:01 2015, 93.0, 84.0, 86.0, 75.0
Sun Jul  5 16:40:00 2015, 92.2, 84.0, 86.0, 75.0
Sun Jul  5 16:50:00 2015, 91.7, 84.0, 86.0, 75.0
Sun Jul  5 17:00:00 2015, 90.2, 84.0, 86.0, 75.0
Sun Jul  5 17:10:00 2015, 89.8, 84.0, 86.0, 76.0
Sun Jul  5 17:20:00 2015, 89.1, 84.0, 86.0, 76.0
Sun Jul  5 17:30:01 2015, 88.7, 84.0, 86.0, 76.0
Sun Jul  5 17:40:00 2015, 87.9, 85.0, 86.0, 76.0
Sun Jul  5 17:50:00 2015, 87.5, 85.0, 86.0, 76.0
Sun Jul  5 18:00:00 2015, 86.8, 85.0, 87.0, 76.0
Sun Jul  5 18:10:00 2015, 86.3, 85.0, 87.0, 76.0
Sun Jul  5 18:20:00 2015, 85.4, 85.0, 87.0, 76.0
Sun Jul  5 18:30:01 2015, 84.9, 85.0, 87.0, 76.0
Sun Jul  5 18:40:00 2015, 84.6, 85.0, 86.0, 76.0
Sun Jul  5 18:50:00 2015, 84.4, 85.0, 87.0, 76.0
Sun Jul  5 19:00:00 2015, 83.7, 85.0, 87.0, 76.0
Sun Jul  5 19:10:00 2015, 83.5, 85.0, 86.0, 76.0
Sun Jul  5 19:20:00 2015, 83.2, 85.0, 86.0, 76.0
Sun Jul  5 19:30:00 2015, 82.7, 85.0, 86.0, 76.0
Sun Jul  5 19:40:01 2015, 81.7, 85.0, 86.0, 76.0
Sun Jul  5 19:50:00 2015, 81.4, 85.0, 86.0, 76.0
Sun Jul  5 20:00:00 2015, 80.7, 85.0, 86.0, 76.0
Sun Jul  5 20:10:00 2015, 80.1, 85.0, 86.0, 76.0
Sun Jul  5 20:20:00 2015, 79.0, 85.0, 86.0, 76.0
Sun Jul  5 20:30:00 2015, 78.4, 85.0, 86.0, 76.0
Sun Jul  5 20:40:00 2015, 78.2, 84.0, 84.0, 76.0
Sun Jul  5 20:50:00 2015, 77.5, 82.0, 84.0, 76.0
Sun Jul  5 21:00:00 2015, 76.7, 82.0, 84.0, 76.0
Sun Jul  5 21:10:01 2015, 75.9, 80.0, 83.0, 76.0
Sun Jul  5 21:20:00 2015, 75.4, 80.0, 83.0, 76.0
Here's what the plot looks like:

Short answer:
The range set via set xrange etc. does only define the lenght of your axes. All points in the file are evaluated (you can explicitly limit this with the index or every specifiers, based on the format of you data file).
Connecting lines are by default drawn if one of the points is inside, but not if both are outside. You can influence both of this with (un)set clip one/two. 
unset clip one does not draw a line towards an outlying pointunset clip two (default) does not connect two outlying points.Switching values outside the wanted range to NaN (== 1/0) like in Miguels answer works as well, but i can hardly see why it'd be necessary.
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