Most of NovAtel's GPS receivers feature an I/O port with various input and output TTL signals, which allow you to modify GPS receiver operations using external TTL control signals. One commonly asked question is how to test the MKI (Event1) to see if it's working properly, versus troubleshooting third party electrical hardware. Here's a simple test for MKI (Event1) functionality: 1. unfold a paperclip 2. short pin#2 to pin#4 on the I/O connector using the paperclip. 3. LOG MARKPOSA ONNEW 4. observe MARKPOSA output once per second. What we're doing here is injecting the 1PPS signal into MKI (Event1), which generates an MKI event once-per-second. You can get fancy and adjust the 1PPS rate using the PPSCONTROL command, then watch the MARKPOSA output frequency change to match your modified 1PPS rate.