may be i can answer this first:
They are for initial SNR setup at a new place for Geodetic measurements.
So it measures the local geomagnetic interference for correction or what?
I think it measures no think, it just indicates simply if the SNR orientation (or alignement) is well ( right), with no offset between him and display scope, because when we put SNR in new location after displacement, we must calibrate his orientaion with instruments in Ynk cabine, we use this instrument for that, to avoid false azimuth indication (real target 240° - SNR Scope 245°: for example!)
Right??
