You are correct. In the first one, I'd suggest spinning the hydrometer a few times and letting it sit until the foam dissipates. The potential alcohol scale is intended for doing this calculation without "advanced math" (i.e., multiplication). It does assume that you have the sample at the same temperature for each reading, though. It's easier to find the corrections for SG (though it should just be a scale by 131 to convert that to a potential alcohol reading).

All the scales on a hydrometer are linear, so it's just a simple conversion to go from one to the other. There's no "wrong" one to read, you just have to know what to do with each number. You can always fairly trivially convert one to another (or just look at the hydrometer and use it to do the conversion for you).