Powder Characteristics Guidebook
Angle of repose, angle of fall, angle of difference, and angle of spatula
The angle of repose refers to the angle between the free surface and the horizontal plane of a powder cone formed by freely dropping powder on the plane under specific conditions. The magnitude of the angle of repose is an indicator of powder's flowability: the smaller the angle of repose, the better the flowability.
When an external impact force is applied to the powder cone formed during the angle of repose measurement, the powder would fall and begin slipping from the free surface. The angle formed between the surface and the horizontal plane after the falling of powder due to external force is defined as the angle of fall.
Subtracting the angle of fall from the angle of repose yields the angle of difference. A larger angle of difference suggests better floodability...
For more introduction, pls see the PDF document below.