In article , Marcus Fox
writes
I'm thinking that those letters are indication of some imperial measurement
of length. R is probably Rood or Rod. 1 Rood is 3.77 metres, 1 Rod is 5.03
metres. C could be Cable, of which one is 185.31 metres, or Chain. There are
two types of Chain, Ramsden and Gunter, 30.48 and 20.11 metres respectively.
C.G. is likely Chain Gunter. Arrow could be distance to some certain point
from that plate.

Extremely unlikely. Distances on the Underground are done in metric,
using km from Ongar as a reference system. Nobody uses roods or rods any
more, cables are nautical, and while mainline railways use the 22 yard
chain, LUL does not.

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