To determine Mag declination:
For example the magnetic declination for Budapest is 3° 58' EAST so the value that you have to enter into config.h is 3+58*(1/60) which is 3.96. EAST means that the value is positive, WEST means it’s negative ( at Pittsburg it is 9° 13' WEST which is 9.21 ). Enter the calculated value to config.h, in the #define MAG_DECLINIATION line, please add an f after the number to indicate a decimal number.
If you didn't get it, it's multiple the second number with 1/60 (~0.016667) and add the first number. You have to multiple first then add. Follow math's Order of operations.
So pino your 10 24 east so that 24*.016667+10 = 10.4f (positive since your east)
