Originally Posted by
kaos joe
I can't add anything regarding the OP's question, but I can confirm that this phenomenon does take place. It occurred when I began mounting a second computer on my wife's bars on our tandems. Had me confounded for a few rides. I now splice the wires together, running both computers off of the output of one magnet/sensor.
Why does your wife want the computer, and do you both look at it and discuss the display?
I use ridewithgps, and it's probably the same in elevation reporting. When I ride over a bridge, it thinks I'm on the surface of the water, so it reports more descending and ascending than I actually do.