# What do you mean by 'active switch' in the manual?
The only active switch we're aware of is the
-[Featherweight Magnetic Switch](https://www.featherweightaltimeters.com/store/p4/Magnetic_Switch.html)
+[Featherweight Magnetic Switch](http://www.featherweightaltimeters.com/store/p4/Magnetic_Switch.html)
These need three connections .. a ground, an input, and an output. Of
the two switch screw terminals on Altus Metrum products, one is