During the result, the are some error that happen while doing the laboratory, considered, the time that use for heat treated it’s not exactly the time that use to be, like the order is 30 minutes but we heat treated it 35 or 40 minutes, Temperature is another factor of error cause we cannot set it equal to 170 all the time because of the machine that work automatically. Measuring the hardness value is considered to cause error due to the worker are not skillful to use the hardness machine.