Keys cannot be cut with one position very high cut beside one very low cut. This maximum difference between cuts is the MACS.
E.g. if your MACS is 7, then a key code 094123 is a MACS violation because 0 and 9 are too far apart in pins 1 and 2. 074123 is OK. See explanation video
Pin-by-pin MACS:
Some specialty keys have a different MACS between different pin stacks. E.g. Medeco has a different MACS for fore-aft, fore-fore and aft-aft, and Mul-T-Lock has a MACS between an inner and outer pin stack but no MACS between pin stacks.
Sometimes a valid key for a lock cannot be removable from the lock when the key is turned. This rule ensures this by ensuring that at some point on the key, the depth increases at least once. E.g. 12345 can be pulled out of the lock, but 12343 cannot. See explanation / example video
GMKs are often made to have one pin at the highest depth so that none of the change keys can be filed down into the GMK.
GMKs are often made to have one pin at the lowest depth so that none of the change keys can act as a bump key to bring any lock on the system to the master shear lines.
This system used a construction key with a ball bearing in pins with thickness .
Using MACS of for master construction key.
Construction keyed systems cannot have a GMK cut below a certain depth in construction pinned chambers. See explanation / example video
Pin
has
depth
Given the information you have about the lock so far, we can impression it to get more information about where the shear lines are. See explanation / example video
This is an interchangeable core system with IC collar on pins with thickness . Using MACS of for master control key.
For certain IC systems, locksmiths are lazy and impose GMK limitations that force a low cut in pins with the IC collar. See explanation / example video
A key with code is known to be a change key.
A known low-level change key often rules out a GMK sharing any of the same depths with it.
If the GMK much be higher than this change key in at least one position, check "System prevents any change key from being filed to a master". Note that this increases compute time significantly.
If the mastered system is a rotating constant system, check "rotating constant". Note that you must know (or vary and trial-and-error) how many pins stacks are constant.
One lock in the system has shear lines (blank for unknown):
If you know the shear lines in one lock on the system, usually by disassembly, enter it here. Enter shear lines with a comma-separated list. Leave a pin blank if you don't have any information about that pin stack. See explanation / example video
Fore/aft for one lock is known:
If you have decoded the lock to determine which pins are fore and aft, enter that information here. See explanation / example video
Bump key works
If a medeco bump key works in the lock, enter its sidebar code here. Capital L and R are full 20 degree cuts, lowercase l and r are half-angle, 10 degree cuts halfway between left/right and centre. See explanation / example video
Photograph shows pins are:
If you can see some info from a photo but not the exact code, enter what you can tell about which pins are high or low cut: See explanation / example video
Photograph shows delta between pin and pin is between [,].
Sometimes from a photo you can't tell the absolute depths, but you can see that some pins are higher than others, or some pins are the same. Interval notation is used, so:
[0,0] is "same depth"
[0,1] is "same or shallower by exactly 1"
[1,1] is "shallower by exactly one"
[1,∞] is "shallower by any amount" (note that any number greater than the number of depths available is equivalent to infinity here)
[-1,1] is "different by no more than one"
, etc. Note that pins need not be consecutive - if you can see by the warding lines that pin 1 and pin 4 are the same depth, it's valid to enter pin 1 and 4 different by [0,0].
If a colour-coded pinning key was used, you can see the pin colours with an otoscope. You need to know what the lock type is, and you need to know (or guess) which pinning key was used. See explanation / example video