That is fairly good. You can but it may vary anyway. In all fairness the RH inside each hide will be different anyway.
For example...
One of my enclosures is showing 64% the cool side hide under this is reading 68% and the warm side hide is 57% it is quite typical all of mine relate to this the cool hide is a bit higher than the ambient and the warm lower.
It isn't super critical in any event, the issue is high humidity and low air flow. If (and it sound like you do not) that is not an issue from 45-70% is perfectly fine. Higher is ok too as long as there is enough air moving. Lower starts to be a concern in the 30% range as this can lead to dehydration. That is a very wide latitude. the real tell is the snake and the shed if the shed is good it is perfectly fine if not is is low. I keep my ambient RH around 60% in the summer it some times creeps up some as it is humid outside too. I never have had a poor shed, I often have sheds in the 55% that are fine and 50% good too. I know hygrometers digital ones if they get too dusty tend to read higher than normal. If you take the specs of some of the popular hygrometers in America (accurites) they are spec'd at 15%+/- meaning if it is actually 50% RH they are considered 'calibrated' if they read between 35% and 65% it is a huge range. If it is off from the start and it starts reading high, the enclosure could be reading 60% but actually be as low as 30%. I have seen lots of posts saying you need over 70% for shedding, my guess is the hygrometer is off and that the real RH is below 40% so adding 20% for a shed brings it to a correct range.
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I have never used any of those three. The one I use is made by Western Instruments I do not know if it is easily available in the UK. I would guess they are all about the same I would not advise the Hair one unless you wanted to do quick comparisons to others they are frail and would not stand up well.
http://www.youtube.com/watch?v=1AMyVUx0Y60