Thanks for the tip, Tiny.  It got my N7 talking to my mouse again.
Regrettably, every time I turn off the mouse or the tablet I lose the connection and have to unpair and re-pair next time I want to use Bluetooth.  It seems to me that Google need to have a look at their coding.
But thanks again for your help -- it solved my problem.

Hello and a Happy New Year to all.
Despite the revulsion that some on the forum feel towards Apple, I am forever grateful to Macintosh, with its mouse and ikons, in 1984 for getting me past the incomprehensible and archaic commands a person had to remember to get the MS-DOS C> prompt to do anything.
I moved from Apple to Windows in about 1994 when I needed to upgrade computers and the Apple to do the tasks I needed to do was going to cost me $7,000+ and I could buy a comparable Windows machine for $3,000+.
Now my smartphone has led me to Android and the Nexus.  It's a delight -- like a lttle puppy dog that can't wait to do what it thinks you want it to do.  Best fun I've had with a computer in a couple of decades.