Altimeter 745 hpa

[Killroy]

Can anyone tell me why (on my 737NG) the lowest possible setting on the altimeter is 745 hPa.

I can appreciate the fact that there must be a lowest value but why is it 745 and not 700 or 800 or 678?

Thanks in advance,

K

[A Very Civil Pilot]

As it's a US aircraft, 745 Hpa converts to 300 inches of water (just about); or 22 inches of mercury, - reasonably even sounding numbers.

That's my guess anyway