Refractometers are fun!

My friend brought me his refractometer to play with. I went to the Farmer's
market today and bought tons of stuff, but it didn't impress with the brix readings. The lemons were 7 whereas whole food's were 6. Everything else was 4-6 except the basil that smelled fabulous was a 2, and the dandelion was a 3! This is disturbing. What do y'all do? Grow your own or find farmers who know how to do it right? Guess I will have to buy a refractometer now. I am hooked! ANd how do you measure beets? I juiced them and dliuted them, but couldn't find a line to read? Thanks for your help.