I was pleased last night to get a fix on the sensitivity of my prototype magnetometer -- on the basis of real results I obtained on Table Mountain this week. While I don't have the equipment to test a magnetometer, I had a graph of multiple measurements which were made in the USA with a standard magnet -- of which I have one. I could calculate on that basis. My previous calculation was incorrect -- it was based on an incorrect formula. So the sensitivity of my design is 7.8 nanoteslas, or 78 microgauss -- at this stage. OBSERVATION: Even with that information in hand, it is not easy to make comparisons, because manufacturers seem cagey or obscure with data. On the surface of it, 7.8 nanoteslas compares favourably with commercial designs. My design, as most of my designs, requires no hard-to-get parts.