Don't you hate it when you reply to your own post, or worse yet, answer your own question
So here's the initial status:
- I insert a 1.5V alkaline battery cell in the batter chamber (with some other things to take up the spare space). The 'low level' meter matches with the Minolta IV F.
- But the 'high level' meter is 1 stop slower than what it should be (e.g. it recommends F/8 when the correct value should be F/5.6).
So I open the meter up to take a peek. To my surprise, there is no potentiometers to adjust. The circuit board is pretty simple, with only 4 resistors.
By trial an error, I find that if I add a 1 KOhm resistor in parallel with one of the 4 resistors, the 'high level' meter becomes correct. The 'low level' meter remains correct.
So now I have a working 1-degree spot meter. It has limited usefulness (unlike films, photos are essentially free) but is fun to play with.