sorry for the multi posts not sure how that happened!!!!
I was allways told the bottle gauges are generally the ones to be most trusted. just so happens I had all mine tested and the bottle gauge is quite a way out. and luckily my hw100 gauge was on. Though generally bottle gauges appear to be the most reliable.
When your next ready to fill, ask someone else to fill it, or go to a gunshop for a fill, and ask them how accurate they feel it is.
Andy