This is not really a 'repair' question; I'm just a bit curious about
something and I suspect someone here might know about it.

My car (2012 Ford Escape) has as it's main gauges a tachometer &
speedometer. Both are needles, and neither has a detente (needle rest) at
zero. Despite lack of detentes, when the ignition is turned off, both
needles go pretty quickly to the zero position without passing it.

About 18 seconds later, both needles 'dip' down (to about -500 RPM & -5
KPH) for a fraction of a second and then return to zero.

Why? If a door is open, that's about how long the interior lights take to
start dimming.