Setting "ASPD_SCALE_1" parameter for Standard VTOL

I am setting-up a standard VTOL, and I came across the parameter “ASPD_SCALE_1”. The description says “This is the scale IAS → CAS of the first airspeed sensor instance”.
My question is: How can I estimate/find the correct value of this parameter for my system?

Thanks in advance!


@Jigyasu You can do a calibration flight on a day when there is no wind and compare the airspeed with groundspeed