For everyone else that notices that COCOM limits require both speed and altitude, the problem is that some manufacturers have implemented these safeguards with an OR rather than an AND. So it’s possible to get tripped up by either limit in practice (unless you know for sure your specific device implements this as an and).
The GPS has to shut off when going faster than a certain speed or higher than a certain altitude. IIRC the GPS maker can decided which they want to follow, and most chose to stop working at high altitude. It’s possible but more difficult to find a GPS that will work with high altitude balloons.
