Calibration:

Nothing beats putting up your flags at home where you can watch what they do in various wind.  Outside the dining room window will give you a chance to see breakfast, lunch and dinner winds.
I try to calibrate all my Wind Indicators to read the same.  At left I put some numbers on one of my standard indicators to give you an idea of how I calibrate mine.  90% of the matches I have gone too I am able to shoot in the 3 - 6 mph area ! (Even the "Crawfish")
When the winds get to gusting 6 to 20 mph then I fall back on shooting the switch.

Below are a couple of pictures from the range last week.

This will give you an Idea of how I set up some of my flags.   The main idea of showing them here was to display two radically different wind conditions that my indicators are not, in themselves, showing.!!! 
When shooting in the wind in the left picture my POI was plus or minus an inch. 
Where as I could expect a 10 or an X when shooting in the wind in the picture on the right.
Take a  look at the tail on my tall flag behind the targets.  The one on the left is Screaming 'Please do not shoot now'