Very, very expensive for a job, almost twice the price of my meter! And it's the cheapest calibration tool ever! My sound level meter is calibrated with a very stiff screw potentiometer so readjustment is probably not necessary. I've checked the calibration a few times since the original calibration and my meter isn't working. So now this tool just sits there. If I get another counter I can use it again. It works, and pretty well. However, this is a rarely used tool and I don't think the cost justifies it.