display scale on right hand side

To answer my own question…

To move the y-axis to the right add this to the shortcode:
chxt=x,r

To add a background of gridlines: chg=20,10

ref: https://developers.google.com/chart/image/docs/gallery/bar_charts#axis_type
and https://developers.google.com/chart/image/docs/chart_params#gcharts_grid_lines

hope this helps others too!

Glad old Tally Graph is still of value. It will of course stop working when Google retires that old image chart API. If you’re a developer willing to help move it to the newer API, let me know!

I have to correct my previous post. It is wrong.

Although my suggestion does indeed add an extra axis to the right, the scale is incorrect.

Another way is to use this parameter:

chxtc=0,-600 (where 600 is the width of the chart)
or
chg=0,10,1,0

These functions draws horizontal lines from the left axis across the width of the chart, so it’s better than nothing!