Gnuplot: how to add y2 axis scale for different units

Question

I\'m plotting data from a file. The data points are in metric units. I want to show a second scale on the right (y2) that\'s in standard units.

The file represents r

Answer 1

It seems to me that the easiest way to do this is to simply scale the data:

set y2tics
plot sin(x) w lines, 5*sin(x) w lines axes x1y2

Of course, you're plotting data from a file, so it would look something more like:

set y2tics
FACTOR=0.2248  #conversion factor from newtons to lbf
plot 'datafile' u 1:2 w lines, '' u 1:(FACTOR*$2) w lines

If you're setting the yrange explicitly (which you may need to do):

set yrange [ymin:ymax]
set y2range [ymin*FACTOR:ymax*FACTOR]

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Finally, if you really want to rely on autoscaling, you're going to need to do some "gymnastics".

First, set a dummy terminal so we can plot without making a plot:

set term unknown
plot 'datafile' u 1:2  #collect information on our data

Now that we've collected information on the data, we can set our real y2range

FACTOR=0.2248
set y2range [FACTOR*GPVAL_Y_MIN : FACTOR*GPVAL_Y_MAX]
set y2tics nomirror
set ytics nomirror

Now set the terminal and plot the data:

set term ...
set output ...
plot 'datafile' u 1:2 w lines