Take care when calculating factors for Cessna aircraft. Pressure error is very large - in the order of 10kts at Vs from memory.
If pilots want to factor by 10% or 20%, use CAS not IAS. You can use the pressure error chart in the flight manual to convert back to IAS. Yes, it does make a difference in Cessna aircraft.
Example, using random numbers.
Vs is 48 KIAS. Pressure error at this speed 8kts. 56 KCAS x1.2 = Vx 67 KCAS. Pressure error is 6kts. Vx is 61 KIAS.