Thanks for the reply.
I did buy 2 HCH-1000 one was dead on arrival. So I cant compare.
Sometimes I do get 3 or 4% different from my WMR-100. When
I compare the two plotted outputs, the accuracy is there but peaks and troughs are at slightly different times.
I put this downs to the wmr-100 being in a sealed space and the
HCH-100 is in moving air.
One example I have come accross for calibration:
An extract is:
Calibrating the humidity sensor
The humidity sensor has a linear output and can be calibrated at two points, 0 %RH and 100 %RH. First modify the code so that the read_humidity() function returns the counter_value by changing the last line to this (return counter_value;). For the 0 %RH point place the sensor in a plastic bag with several sheets of absorbant kitchen paper that have been dried in the oven for an hour. It will take some time for the humidity to stabilize, so be sure to wait for it to stop changing. For the 100 %RH point place some warm wet paper in a plastic bag with the sensor, taking care not to get the board or sensor wet. Once agian it will take some time to stabalize. When you have the two counter readings you calculate the conversion factors and change two variables in the code.
I dont dare try this at the moment for fear of killing another $17.