Martin Purdy of Upper Hutt, New Zealand writes:

I have a copy of Biggs, bought some 20 years ago.

1. Norman Biggs, "Apothecaries Weights: An Outline Catalogue" (White House Publications, 1994) - 32 pages ISBN 1898310017,9781898310013
https://books.google.co.uk/books?isbn=1898310017

2. Daniel Vangroenweghe & Tillo Geldof, "Apothecaries' Weights (Pondera Medicinalia)" (Centre for the Study of Apothecaries'Weights, 1989) - 268 pages
https://books.google.co.uk/books?id=spCxHAAACAAJ

The symbol for dram or drachm (?) resembles a flat-topped "3", possibly relating to the fact that it was three scruples(?), but it alsoseems to resemble a script "z" - "z" was used in abbreviations (such as "oz" for "ounce") and even toindicate the word "and". The ounce, though, seems an extension of this: ? See also
http://www.textcreationpartnership.org/docs/dox/medical.html

P.S. The convention was sometimes used, for a final "i" to be written as "j".

An on-line catalog:
https://www.apothecariesweights.com/catalogue/

Also this descriptive page:
https://www.samhs.org.au/Virtual%20Museum/Medicine/
Apothecary_scales/Apothecary_scales.html

and this downloadable on-line 20-page booklet, posted about 4 months ago:
https://archive.org/details/CONA2019FebruaryPresentation

To read the earlier E-Sylum articles, see:
BEAUTIFUL AND UNUSUAL MONEY : Two Scruples Apothecary Weight(https://www.coinbooks.org/v22/esylum_v22n24a31.html)
NOTES FROM E-SYLUM READERS: JUNE 23, 2019 : More on Apothecary Weights(https://www.coinbooks.org/v22/esylum_v22n25a10.html)