Knowledge Base:  

Knowledge Base : APRS Position
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Position Comment - Custom... not really
On the Yaesu FTM-400 and similarly (but not identical) in the FTM-100, there are options in the Position Comment that are called Custom 1, 2, 3, etc. So, while they are "Custom" in name, they are not
Navi - not working, radio stays in standby

"Navi" won't work, radio stays in "Stdby" - Radio needs to be set to GPS.  Go into "Radio Menu Settings", select the APRS/GPS tab, in about the center of the page, "My Position" needs to be set