(idm) lock grooves

From Irene McC
Sent Tue, Jan 5th 1999, 09:24

On 4 Jan 99,  Joanisse, Robert wrote:

> how to use a razor to cut up
> the last groove on a record into a lock groove.

Never having seen a lock groove, could somebody please explain 
how these work?  Does the needed somehow return back to the 
beginning and repeat play until you physically move it off?

I
*