The analogue meter is programmed in the status PIC to have serial data of 0 to 54 displaying S0 to S9.
The calibration on transmit speaks in terms of dB over S0 because numerically this is what is sent to the status PIC.
My Picswr analogue meter calibration specifies 0.4w per 'dB over S0'
Thus the S9 position on the analogue meter will correspond to 0.4 x 6 x 9 = 21.6w. ( 6dBs per S point x 9 S points).
Above S9 the G6AK calibration is more compressed ... but this is dealt with by making a calibrated scale for the meter.
The SWR calibration is fixed at 0.25 units per LED, ie:
LED 1: SWR = 1.0 LED 5: SWR=2.0 LED 9: SWR=3.0