Ion Petroianu, VA3NOI
If you do not require calibration to a standard I would suggest you set your lowest value (mine is set to 2) and your highest value (you measured S9 at 50 uV in that gives you 1.6 V) at one third of 254 (82 to 85) and select one of the samples. I liked sample 3 and my highest value is set to 80.
The software will calculate intermediate values for you.
Encode and write to uBitx.