They only measure on one side. Its not a complete body inches lost, it's an estimate based on the beginning measurements they take. They should measure the same side every time though. I know they do my right side because it's my dominant side.
Also, try to remember where on your torso they do those measurements so that you can help get the tape in the right place. I know that I only get measured once a month or so and they measure people every day, so how can i expect to remember where on my body the tape should sit. I'll remember for them
Hope that cleared it up a little.