Generally accepted is the fact that even a simple hair hygrometer that one can build himself , as http://www.inrp.fr/lamap/activites/objets_techniques/idees/technique/a ir_vent/hygrometre.htm is accurate at 5% once well regulated. I have such a commercial system in my workshop (with a tall 25 cm hair) to add a little internal pressure (with an air drier) when the humidity is too high (it flow dry air in the place from another room) The system is very reactive and I feel I can maintain the wanted environment (around 50% actually) What I don't get is that the different electronic hygrometers I have all give readings that look similar at 5% or 7% more or less. I suspect that the accuracy of the electronic systems is may be good in a little medium zone, but far less in the high and low ranges I believe too that the capacity used in the cheap circuits find in the hygrometers and such electronic devices, is always reacting the same way, and differently than hair hygrometers that gives too another reading that a psychrometer. Richard, may be chiming in, as he seem to be knowing more than me about these facts. Mostly they may be more precise at a certain temperature level than another, we are asking an actually very small element to react to difference of tension induced by the absorption of humidity, and this change with the air pressure, the temperature... This is asking a lot to these small parts. Psychometric measure can be done with only one thermometer, and 2 readings, one wet and one dry. Did not do that really, but I understand the psychrometers are the tools used for the weather prediction, so they are accurate. Regards, Isaac OLEG
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