Calibration Drag and Drop ( +/- ) 1 level only

Dears.

Im working on Calibration, and activated the Drag and Drop functionality.

However, im being requested that the Drag and Drop shall be restricted to moving employees ( + / - ) 1 Level only.

Example : An employee with rating 4 you can move either to 3 or to 5 only.

Is this possible? and how?

Appreciate your support!
Regards, Jad Atie