Clarion NX500 nav
 

Hello everyone.
Just joined hoping this forum can address an issue with my unit. I have this NX500 in my hot rod and it's awesome. But when I use the nav screen to view my speed the digital readout does not match the sweep gauge which is on the same screen. When I'm doing 61 mph on my in dash analog speedometer, the NX500 reads 110 kmh on the sweep part and 100 kmh on the digital part. That's why I'm confused coz the unit is using the same gps function. The discrepancy is relative to the speed. That is, the higher the speed the bigger the discrepancy.
So, any input that can help a retired cruiser?