My input to gnuplot looks something like this:
1:00am 1 10
1:00am 30 12
1:01am 60 18
1:01am 90 20
1:02am 120 21
...
The first column contains (what I'd like to be) the X-axis labels, while the second column contains the X-axis values. (In actual point of fact, I have one row per second, so many rows have '1:00am' as in the label column, then '1:01am', etc).
I can plot the values I care about using something like:
gnuplot> plot "my_data.txt" using 2:3 with lines
And I can set the X axis to have a tick (and label) every 30 minutes (which is 30 * 60 = 1800 seconds), but the label it uses is the X axis value (something like 3600 for one hour).
What I can't get is for the labels that show up under each tick to use the values from the first column. I can't even find anything that looks promising in the gnuplot manual. I've got to assume this is possible, I just don't know where to look.
Edit:
Progress, I've discovered the xticlabels() parameter to plot. The problem is that it seems to plot these labels for every xtic (that is, one per second in my data set), rather than at the intervals defined by set xtics.
Edit and Answer:
Turns out gnuplot has support for graphing time-series data. For the curious:
set timefmt "%H:%M:%S"
set xdata time
This causes the X axis data (once reformatted to match that pattern) to be interpreted as time-series data. This is then combined with
set xtics 3600
Formats the X axis as I described.