We thought it was in degrees too. But after rotating it to 57º, using AnglePlanes Plugin and rotating to the same angle using Reformat, the results aren’t similar.
I confirm that it is rotation in degrees. Note that rotations are incremental: if you rotate around multiple axes, the previous rotation slider is always reset to 0.
These angles may refer to the same rotation - they are just different angles of the same triangle: 57deg = 90deg - 32deg (-1deg probably measurement error).