Tweak GAIN_STEPS calculation in celestronaux.h (#1255)

* Refactor GAIN_STEPS calculation in celestronaux.h

Updated GAIN_STEPS to a new calculation based on geometric analysis and testing.

* Update GAIN_STEPS calculation in celestronaux.h

The factor in here must be inverse to the one in the simulator - so 10125/128 ~ 79

* Fix scaling factor calculations in celestronaux.h

Author: jochym

indi-celestronaux/celestronaux.h

@@ -507,8 +507,17 @@ class CelestronAUX :
         static constexpr double STEPS_PER_HOUR {STEPS_PER_REVOLUTION / 24.0};
         static constexpr double HOURS_PER_STEP {24.0 / STEPS_PER_REVOLUTION};
 
-        // Measured rate that would result in 1 step/sec
-        static constexpr uint32_t GAIN_STEPS {80};
+        // Measured rate that would result in 1 step/sec - only approximate
+        // static constexpr uint32_t GAIN_STEPS {80};
+        
+        // Rate based on geometric analysis and testing against SkySafari 7, simulator and real mount:
+        // Logical unit for guiding commands is 1/1024 arcsec/sec.
+        // Steps per arcsecond = 16777216 / (360 * 3600) = 16777216 / 1296000
+        // Scaling Factor (Units -> Steps/sec) = 1024 * (1296000 / 16777216)
+        // Factor = (1024 * 1296000) / 16777216  = 1327104000 / 16777216
+        // Simplified Rational Factor = 10125 / 128
+        // Steps/sec = Value * (10125 / 128) = Value * 79.1015625
+        static constexpr double GAIN_STEPS {10125.0 / 128};
 
         // MC_SET_POS_GUIDERATE & MC_SET_NEG_GUIDERATE use 24bit number rate in
         static constexpr uint8_t RATE_PER_ARCSEC {4};