I recently had to return my Surveymaster for repair, and while talking with the tech I asked if there was a remote pin sensor available with a longer cord. He said not, but that I could just make up a extension cable of whatever length I needed, and them compare the results obtained with the factory and home-brew cable to calibrate results from the latter. I can think of a lot of various kinds of "sensors" based on this technique - if you need to confirm a reading you could them use the meter directly.