Diaphragm and driver marking match?

Dear all,

It has probably been debated but I can't find it.

Please remind me about the hand written marking on the 4" drivers and diaphragms. They typically range from "-5" to "+5" I think.

Is "+" a phasing plug that extrudes further backward from the core, or the other way around.

Matching the numbers is probably the best but if not available (limited supply of diaphragms) is it better to have a higher number on the diaphragm, ie a "+2" diaphragm is less prone to make noise in "0" core than a "-2" diaphragm? How big is the height increment between the markings?

I'm having a difficulty to a pair of 2451 with SL dia's to measure them same over 10kHz

If discussed before please post link.

Kind regards
//Rob