On your computer, or RetroPie

to setup a game in MAME the spinner needs to be adjusted
from 1 thru 255 where 100 is 100% or 1-to-1, no change.
UltiMarc & Groovy Game Gear Spinners both run at 1200 PPR,
the Chinese Rotary Encoder(600 PPR) Quad output is programmed to 1200 PPR as well.

To make a change to Game sensitivity:

• Open the game
  
• Press <TAB> on keyboard
  
• Select ‘Analog Controls’
  
• Select ‘Dial Sensitivity’
  

              Orig. Spinner PPR
Adj % = ————————–    x 100
              Your Spinner PPR

List of Games Adj %

Major Havov has a special rare Roller controller, a video from John’s Arcade showed a close-up of Urethane rubber wheel in contact with metal roller which drives the pin-wheel (24T) optical sensor. This is similar when determining a Trackball’s, Ball to Roller diameter ratio giving a ‘gear-up’ drive to affixed pin-wheel. Calculating the ratio, you toss out the value for 𝜋 (circumference = 2𝜋r or 𝜋d) or any video image scale.
The ratio measured on my monitor (scale 1½ to John’s thumb) was 3.250” / 0.625” = 5.2 x 24T = 124.8 PPR approx. (±5% Error)
Measurement #2: 2-13/16 & 9/16 or 2.8125” / 0.5625” = 5.0 x 24T = 120 PPR approx. So between 120 and 125 PPR.

Video on ‘Accurate Spinner Sensitivity in MAME’