Robbing can be distinguished from a nectar flow in that it only lasts a day or two, has little evaporation loss at night, and occurs when nothing is coming in.
Example 1 Athens, GA 2018
This example is from Athens, Georgia, USA on June 30, 2018. Nothing was coming in - there was only metabolic loss for the three days prior to the robbing and the three days after the robbing. This hive gained over 20 lbs in one day!
One day graph of the robbing. Notice the linear increase that continued until sundown and the lack of weight loss due to evaporation at night.
Example 2 Bend, OR 2018
This example is from Bend, Oregon USA on September 8th and 9th, 2018. During the days prior to the robbing, there was a little coming in as the hive was maintaining it's weight. This may be pollen as there is little evaporation loss.
Example 3 Scaly Mountain, NC 2012
An accidental experiment where a partial super of honey that had been pulled from another hive with the intent to feed weaker hives was left uncovered. When the robbing from the uncovered super was discovered, the super was weighed several times.
Tue Apr 3 10:45:00 2012 Bees. robbing 21 lb gross deep from Athens meant for another hive. Oops. Tue Apr 3 12:05:00 2012 Super now weighs 17 lbs. So this is what robbing looks like. Pretty impressive. Tue Apr 3 13:20:00 2012 light rain started Tue Apr 3 13:55:00 2012 Super now weighs 15.5 lbs. End of experiment Tue Apr 3 15:10:00 2012 hard rain