In reply to Al Evans:
Hi Al
I don't have the guidebook but if I dredge my memory I think I can outline the broad framework of the grading system, if that's any help( I'm sure you're already familiar with it, and are thinking of the general interest). First a few examples, taken from the CC's New Climbs 1968:-
The Writing on the Wall 5b 3/0/0/1 Hard Very Severe
The Last Gasp 5b 4/0/0/1 Hard Very Severe
Krapp's Last Tape 5b 6/0/0/1 Hard Very Severe
The Bilk 6a 4/0/012 Extremely Severe
(a couple of errors here; the route described is actually The Blik rather than The Bilk, and something's clearly wrong with the numbers - probably either 4/0/0/1 or 4/0/0/2)
The Mal - main pitch 6a 7/0/0/2 Extremely Severe
- top pitch 5b 3/0/0/1
Direct Start Hell Gates 5b 3/0/1/1 Hard Very Severe
Last Slip 6a 7/0/0/2 Extreme
Little Red Rodney 5b 1/0/0/1 Hard Very Severe
Spinor 6a 6/2/2/3 Extreme
Limbo 6a 4/0/0/2 Extreme
Clan Union 6a 4/0/1/1 Extremely Severe
S.O.S. 5b 1/0/0/1 Hard Very Severe
The adjectival grade and the initial technical grade will already be familiar. This was well before the introduction of E grades, so HVS and Extreme were the top two levels. As, in modern terms, the hardest routes were probably around the E3/4 level, the HVS grade, if used to mean "a bit easier than Extreme", could easily be modern E2! I've copied this more-or-less verbatim; the grades Extremely Severe and Extreme were exchangeable and meant the same thing in general use at the time, and I assume the same was the case with Drummond. The use of the 6a grade might appear a bit generous, but note that there are no 5cs. The 1964 edition of John Nixon's "Limestone Climbs in South West England" shows that technical grades were already in use; he uses IVa, IVb, Va and Vb. I think that 5c was a later addition, meaning that all the old 6as would have been given 5c a few years later (I seem to remember that a Welsh listing from Drummond at the time gave Vector 6a and The Strand, of course, 6b; again, if you add in 5c and shift everything down these don't seem quite as overblown as they might now appear).
Which brings us to the other bit. The first figure simply denotes the number of crux areas; in some cases this looks quite high, but makes more sense when you think of a typical Avon pitch involving a whole series of small overlaps, many of which could offer individual cruxes. This did, I suppose, give some indication of a route's sustainedness, though not necessarily in the strenuous manner of, for instance, the later Arms Race and its neighbours. The last three figures put a grade on three other factors, ranging from 0 at the "nice" end to, I think, 3 at the "nasty" one; these were - and I think I have the order correct - protection, rock quality (ie solid or otherwise), and a harder to define indication of the type of climbing, with particular reference to positiveness/precariousness. The first two are simple enough; we nowadays have, variously, P1-3, R/X, S1-6/R1-6 to describe a route's protection, and 0=solid, 3=rubbish is easy enough to understand. Drummond went to some length to define the different levels in the final category; 0 would have meant something like "obvious moves on positive holds", while 3, if memory serves, he defined as "persistently thin, limiting climbing, with resting only at protection"! Make of that what you will; "thin", while used less these days was, in the past, common when describing precarious climbing, so maybe we should simply regard that final number as a measure of a route's "falloffability". I've no idea how he would have applied this grade in other parts of the country; in The Peak, for instance, would a typical Stoney route like Our Father or Wee Doris - thuggish but with positive holds - have been accorded a lowly 0 or 1, while an easier but more precarious one like Great Slab a 2 or 3? Presumably so. The bit about "resting at protection" does not, I am sure, mean hanging on it, but simply refers to the familiar phenomenon whereby it magically becomes much easier to rest in a precarious position as soon as you get some gear in. Finally, some of the above examples that are nowadays considered to be quite bold routes seem to get a surprisingly low protection rating (ie meaning well-protected). This is probably due to more, and newer, pegs back then; the description for Krapp's includes five.
Although obviously somewhat unwieldy, I was always rather baffled by the accusations of incomprehensibility that were frequently levelled at Drummond's system; it's not rocket science, mostly! I suspect that such accusations were less a case of inability to understand, than unwillingness.