P L & R

I checked on the Precancel Stamp Society website, but couldn't find an answer.
What does P. L. & R. mean?



Thanks

PL&R = Postal Laws and Regulations.

Here's an envelope cut square (precanceled) that recites the same 562 P.L. & R.:

Knowledge is power. Thanks much!

useful link re Sec. 562 P.L.&R

http://wesewretro.com/2011/11/how-t...ng-patterns/

That's a nice link to date Bulk Rate Mail. Now for an advanced question:

The previously posted link identifies 435-1/2 P.L.& R. as being pre-October 1, 1932;

562 P.L. & R. as between October 1, 1932 and February 25, 1949;

34.66 P.L. & R as between February 25, 1949 and December 21, 1954; and

Blk Rt. (Bulk Rate) as post-December 21, 1954.

But where does 34.65 (e) P.L. & R. fit in? Must have been a different regulation in the 1949-1954 range, but what was it for? I've never been able to figure it out. Here's the meter to prove it:

Never mind. Just found my answer on another web site. It was for Non-Profit Org. mail, apparently in my example between July 1, 1952 and July 1, 1954, a relatively short period of usage:

http://rdhinstl.info/prexies/1bu.htm