So, the speed point would be..

125 = 0.8 / Hm

multiply both sides of equation by Hm... 125 Hm = 0.8

divide both sides of equation by 125... Hm = 0.8 / 125

Hm = 0.0064

Likewise, the metered point would be...

Hg = 0.064

Ten times... Seems extremely arbitrary or lucky to be such a round easy to remember number.