how long have these watch size digital bike computers been around?

When I started commuting 2 springs ago I went up to wally world to get one of those old time big analog speedometer and to my surprize they had these little watch size digital bike computers.
I had not been on a bike for 20 years and I was riding a old huffy that had been sitting in the garage for 10 yrs. only 6mile round trip. since then i've discovered real bikes and My LBS.

Just wondering how long the bike computers have been around.