[78-L] Any tips for reading (or rubbing) matrix numbers?

[Doug Caldwell]

I find Aeolian Vocalions (c. 1919) particularly difficult -- have been using
old Air-Mail paper (very thin, like tracing paper) and a pencil; sometimes
verifying with a magifying glass.

 

Any tips or trick-of-the-trade?

 

Doug Caldwell