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From: sfeam <sfeam@users.sourceforge.net>
Newsgroups: comp.graphics.apps.gnuplot
Subject: Re: alignmnet values xaxes and x2 axes
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Date: Sat, 17 Mar 2012 23:43:25 -0700
Organization: gnuplot development team
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Klaus Dahlke wrote:

> Hi all,
> I use Gnuplot 4.6 on Linux with either x11 or wxt terminal.
> I have a dataset consisting in 4 columns (analyzing workouts):
> time run [sec], distanced run [m], pace [min/km], heart rate [-]
> ...
> 180, 500, 06:00, 140
> ---
> 360, 1030, 05:57, 145
> ...
> 540, 1555, 5:58, 144
> ...
> 
> Points are taken every 3 seconds.
> I'd like to use 'time run' ans x1axes and 'distance run' as x2axes in
> such a way that when I position the mouse at e.g. x1=180 sec the info
> shall show x2=500, position at x1=360, the info shall show x2=1030. 

Both the x1 and x2 axes are linear, so unless there is a perfect
correlation between your "time run" and "distance run" values it
is not possible to have them all line up perfectly.



> I didn't find the trick to get that in an exact manner. With some minor
> deviation it is achievable when set x1range and x2range to the
> respective min/max values. Autoscale will bring some larger deviation.

The command "set autoscale fix" will prevent autoscale from adding any
extra range to the axes.

> Is there any other trick to align the two x-axes to the values of the
> datafile?

If the values in your file are not perfectly correlated then nothing
you do is going to make them line up perfectly.

If it's just a question of having both values labeled for each 
time point, you might try:

set datafile separator ","
set xlabel "Time"
set x2label "Distance"
set xtics
set x2tics
plot 'file' using 1:3:xtics(1):x2tics(2)

The labels along x2 will be correct, but the axis will be slightly
non-linear.


> Thanks,
> Klaus