Just found another Sowerby measure. Pattern number 1470, pg35 1885 pattern book. Made in four sizes.
This one is 3.5" (9cm) tall, so may be the smaller of the four.
One side is graduated 1,2,4,6,8 and marked f3.
The other side is marked 1/2, 1 and marked f3, but the 3 has the top line repeated, see picture. Very odd.
This was done in the mould so must have been intentional.
Anyone know what these marks mean, or what the measure was used for?
Mike