[r-t] Extension

[Robin Woolley]

Don's comments in the first post of Issue 2 reminds me that, in the 
original version, what was entitled 'pivot bell sequences' were 
preserved. This just is another way of saying place-bell order was 
preserved. This would immediately rule out Bristol S Max (but not the 
Royal), since BS8 is gp MX but BS12 is gp J.

In simple terms, if you ring a gp A parent, in which place bells (from 
2nds) increase to a peak and then return to 2nds, you *might* 'produce a 
method acceptable to the practical ringer (not so much the 
mathematician) as the obvious extended form of the parent' rather than 
an extension in gp B, say, where there are two 'peaks'.

Plot a graph of place-bell against lead-number and you will see what I 
mean. Gp C has three peaks, etc; gps F, G and M 'look' like gp A, etc.

The 1952 report says " if the structure of a lead of an extension be 
satisfactory, the “likeness” of the blue-line of the extension to that 
of the parent will be governed by the order in which the leads are 
joined together" and a table gave the instruction that, in effect, group 
letter must be preserved by selecting the appropriate pivot-bell sequence.

Best wishes
R