How are you measuring your salt levels?

On my SWCG, I get different readings all the time. But over time, I take the lowest reading that pops up with consistency to be my "true" reading. Also, when I've taken water samples to the pool stores (samples taken at the same time and place from my pool), the pool stores give different readings for my salt level. So, I take their salt meter readings with... wait for it ... a grain of salt!