I’m not much help. I really wish that there was an international standard for the units of measurements. France doesn’t use mg/dl but g/L which means a 101mg/dl is 1.01g/L or 5.7mmol/L.
I don’t have personal experience with the Blue Jay GTS watch, but it may be stand alone. I think the problem is going to get it to display different from what is sent to the watch.