The Cereal & Grains Association (formerly AACCI) have published approved methods for evaluating wheat flour for falling number. AACC Method 56-81.04
Determination of Falling Number. I no longer have a membership with Cereal & Grains to provide you details of the method.
The description is: Objective
This method is based on the ability of α-amylase to liquefy a starch gel. The activity of the enzyme is measured by falling number (FN), defined as time in seconds required to stir and allow stirrer to fall a measured distance through a hot aqueous flour or meal gel undergoing liquefaction. α-Amylase activity is associated with kernel sprouting, and both of these are inversely correlated with FN. The method is applicable to both meal and flour of small grains and to malted cereals.
I am not aware of a correlation to Units per ml for amylase activity. Falling number is the activity evaluation method.
In the US malted diastatic barley flour is added to wheat flour on the flour mill, based on QA guidance, to target a falling number activity specification range. In Canada this is also done by adding amylase enzyme in the treatment at the feeder.
I will ask a former colleague of mine in the flour milling industry for further input, or guidance and see what we can come up with. I hope this is helpful for starters.