Does LPP Mean an Incomplete RCM? However, in 1982, when it was being dis- cussed as a method, Wiegend Jensen made the observation that in effect, LPP was sim- ply an incomplete RCM system, because, as noted above, either you are progressing all the positions or you are not — and in this case you are not. This belies the truth, however. A partial progression system (or LPP, by today’s naming convention) used various levels of incidental master keys. If, for example, four chambers had been progressed, then the acting top master key for the system had the potential below it of (assuming two increment system for simplicity of explanation, though the equivalent would apply to single increment) four page (three pin) master keys, 64 verti- cal column master keys (VGM – two pin), 4 under each of the 4 page masters, and 256 Block (one pin) master keys (16 under each page master, or 4 under each column master). Why is this an important distinction? Aſter all, they are the same as they would’ve been were this a total position progres- sion, except that there are no higher keys involved than the (in this case) four pin master key. Right? The answer to the importance of this lies in one of the primary differences between a TPP (total position progression) and a pure RCM (rotating constant method). system. One of the advantages the TPP had over the pure RCM was the relative ease of assigning master keys of various levels. If you’re at all familiar with RCM, you should be well aware that the RCM makes master key assignments much more com- plex — to the point that most experts rec- ommend not using them or limiting their use to certain specific ones that are more recognizable and predictable. This has made the pure RCM a relatively unused option for most master keying locksmiths. However, this isn’t the case with a partial progression system (LPP). If we were to ex- WWW.ALOA.ORG “In the limited rotating constant (LRC), we limit the number of positions being progressed for individual key bittings. Certain positions will never be progressed to specifically create individual key bittings.” pand an existing LPP system to a full-blown RCM, we would have unintentional key interchange almost everywhere we looked! Therefore the LPP (or partial progression) is not simply an incomplete RCM. Yet, by the theory that either we are pro- gressing all the chambers or we are not, it would seem that it definitely is related to the RCM. That is the distinction I would like to see you accept in order to begin true discus- sion of the possible techniques we can use in master keying. Key Definitions While there are only two overall methods, there are many techniques within at least the RCM method. The definition of RCM, according to the LIST Council dictionary, is: rotating constant method. n. a method used to progress key bittings in a master key system, wherein at least one cut in each key is identical to the corresponding cut in the top master key. The identical cut(s) is moved to different locations in a logical sequence until each possible planned position has been used. The important phrase in that definition, for the purposes of this discussion, is “each possible planned position.” We do not have to plan to use every posi- tion. Locksmiths have always acknowledged that there were variants within the RCM, such as three in five, four in five, etc. What we are stating here is that there are other variants as well, and that the limited posi- tion progression, or LPP (formerly known as partial progression) is one of them. The LIST definitions are: LPP. abb. limited position progression Limited position progression. n. a tech- nique within the RCM where only one pattern of progression is used for the entire system. But a more specific definition for the pur- poses of this article might be: Limited position progression. n. A variant of the rotating constant method wherein only a specific number of chambers have been, or are planned to be, progressed, with no actual rotation of the constant positions. Now, I will be the first to raise the ques- tion, if we are not rotating the constant positions, how can it be a rotating constant system? This has been my unanswered ar- gument since the topic was first breached in 1982. LPP had been the primary method of master keying, implemented extensively from 1963 on, but because of that definition, was no longer taught under the guidelines of the LIST Council’s predecessor — the ALOA-sponsored National Task Group for Certified Training Programs, Master Keying Study Group. This was simply based upon the assumption that either you are progress- ing all the chambers or you are not. But here we see a new dilemma because it would have been equally simple to real- ize the rule that either you are rotating the constant positions or you are not. The argu- ment could be made that therefore the partial progression or limited position progression is actually a third method. But if we begin down that rabbit hole, where do we stop? There are other variants as well. Do we want every technique to be- come listed as a separate method? That seems overwhelming, at least to me. So for now, let’s just accept that the LPP is a variant of the RCM. Aſter all, we are not talking a difference in how we do it, only a difference in how we think of it. Regardless SEPTEMBER 2014 KEYNOTES 11
