The SI unit of angular acceleration (rotary acceleration) is radiant per squared second (rad/s²).
1 rad/s² is the angular acceleration of a body whose angular velocity changes during a time of 1s evenly to 1rad/s.
The SI unit radiant (rad, unit m/m or 1) indicates that the angle is specified in radian measure.
In addition 1 rad has the size of that angle, which gives a bow b with the length of the radius r, so b = r.
The full angular has 2π rad = 360 degrees;
At rotary acceleration sensors the torque is measured which acts on a mass put into rotary motion (is accelerated).