I meant that the meter I bought would be useless in terms scale, not error.
I matched the sensor module, circuit, and meter so that it would be easy to read. 1.0V=10A, 2.0V=20A etc.
If I changed the gain, not only would I need a meter that reads different voltages, but I won't get the nice 1:0.1 proportion which allows me to use the existing meter 'face'. I wanted this to be simple; It's supposed to be a quick hack, not a huge project.
AC is not part of the intent. With AC, RMS values are more useful anyway, and I don't even want to go there. I will mostly use this for testing automotive applications, but if I really want to see some AC, I can just stick some scope or DMM probes directly on the sensor output, right?