Hi - in case any of you were wondering, I have now passed my CITB. (Huzzah!) However, I was checking through my Safe Handling of Refrigerants Reference Manual today and found a reference to the degree of acceptable vacuum you should aim to achieve. It states " as a guideline at least 10" Hg, 250 mm Hg vacuum should be achieved".

I thought that the general guidance was that a vacuum of 300 to 500 microns should be achieved. Am I being thick, or isnt 300 microns equivalent to 0.3 mm Hg / Torr ? If so, the CITB guide is recommending a vacuum of 250,000 microns... I am totally unfamiliar with the whole concept of microns, mm Hg etc, so if I am totally missing the point, please tell me!!