Pinpoint calcium monitor

[Ruth]

Has anyone tried one of these? I bought one and have tested both my large systems. With the monitor - actually it is more of an electonic tester as you don't leave it in the tank - I am getting calcium readings at least 30ppm less than I do with my Salifert test kit. Now I don't know which is off. I'm not totally confident that I have the monitor calibrated correctly so I am going off the Salifert test.