If you refer to Mizar-24, I have one. You still need to test with the stone & file.
The M-24 will round to the nearest karat designation. If you have 12.5k it will read 14k & so on. It will also give @ times a false reading, for example, if you are testing a gold alloy,it could read 10k when in reality it's not 10k.
I bought some 370g of gold alloy wires. I tested with the M-24 & it read 10k. The seller told me material had been tested before & that it was "plated". So I bought as plated, & he was right. I recovered 9g of gold.
Ever since, I don't rely on the M-24.