Was think'n when you are in the mode of displaying the voltage, maybe something like you do now, not sure, but a press&hold in this state or something would trigger a config mode, then simply press 4 clicks, then 18 clicks for 4.18V for example. Now 3.98V would be a total pain. Not sure if you go to 100ths, but I do in NarsilM. Again, I'm probably overly precise (i.e. anal) about the accuracy but it's nice knowing. I don't blink out in 100ths but measure and calibrate to 100ths. My DMM's all go to 100ths. Bad/weak batteries under load will drop, but in normal voltage blink out mode, I find the battery measurement to be accurate.
Same could be done for calibrating temp - when blinking out the temp, same sequence in the UI would trigger config mode - I would optimize clicks though, break them down per digit, so 24C entry is 2 clicks, then 4 clicks, instead of 42 clicks. A pause would be the trigger between digits, then we blink, then the user starts the next digit.
Maybe the digit trick could be used for the 3 digits of voltage, not sure. I kind of like using a cell that somewhere between 4.00 and 4.20 though so it's a max of 20 clicks. Maybe for consistency, per digit, or is more consistent for both temp and voltage to be 2 sets of #'s? Dunno.
I tell you though, when you get the calib dead-on, and see your blinks follow a rounded value of voltage -- 4.15V blinks 4-2, then 4.14V blinks 4-1, its pretty cool. Yea, I know, anal, but I just got that perfection in me - math over creative, 750 in math SAT, 540 in English SAT, German heritage. I really think somewhere in my ancestry I had a watchmaker or mason who spent their entire life trying to achieve perfection, died poor... Well, that might be the story of my grandfather as a house painter in Manhattan - high end work, never made decent money at it though