0 set calibration

I would like to implement 0-point calibration with a button.

I have loaded the suspension strokes into App.
I want the stop to calibrate the stroke value (ex 20mm) as 0mm and return a negative value if the suspension extends.
I thought I could use the button function set value or set value(fomla), but is there any other better way?

For this you need to set a Dash Data X value to your current stroke value and then have gauges that show stroke - Dash Data X. Recommend using Dash Data values instead of Dummy values as Dash Data values are saved between instances.