Many have sat-navs. How many have sat nags?

You mean like those things that say "As soon as possible, make a u-turn [you navigationally challenged idiot]"?

I have a friend who calls the device a "sat nag", and some were; but mine is too polite for that.

It doesn't try to tell you off when you disobey its instructions to take a route you know is actually a lot longer than your intended, and clearly signposted, way.

It tried that a few days ago, when I switched it on far earlier in the journey than I really needed. It decided my choice was the better and went with it, barely a hundred yards past the turning I wanted and used.

Anyone with a wife...