Sicura Chrono Computer

Late 1960's or early 1970's? Not sure.
This is very big for the times, 47mm. X 45mm., two internal rotating dials controlled by the two left crowns, one external rotating bezel slide rule.
Centre orange minute hand continually runs and resets to 12 via the upper right red ringed crown, a la "chronostop", offset sub-seconds dial with orange hand.
Hour and minute hands are scuba style and, along with the hour markers, glow brightly after being in strong light. They are set and watch is wound by bottom right crown.
Heartbeat is provided by a Bettlach EB 8806 17 jewel hand-wound movement, and runs strongly.
Got this from an old friend in exchange for a silver pocket watch, I know I got the better deal even though he thinks the same.
What is it for?
Why is it so big?
Why do they sell for such large amounts ($500+ for good examples)?
Why does my arm hurt after wearing it?
Why am I asking you?
Are you even reading this? :-D

Thanks for looking, and hope you like it.
Bob.