Pete,
As a quick aside... "HighJack"

A lot of Rebreather divers here in the US dive with 10/52 as a standard dil. for dives in the 120 fsw - 270 fsw.
1) Very easy to mix... fill bottle half with He and top with air.
2) Very simple to calculate expected FO2 with for a full dil. flush.
3) The O2% is low enough to make a real difference when flushing at depth to address a high PP02
Dive Safe
Mark