pstaney is right, but as most people are not usually very proficient with their .57 times table for mental arithmetic, multiplying by .6 does the trick, with just a small tad of conservatism for a climb (the opposite for a descent).
Very useful to fly a SID gradient accurately if you have Flight Path Angle (or Flight Path Vector) indication, and better yet if this angle is selectable as a Flight Director function. I use it all the time.
Regards,
Old Smokey