Shetland 2 ply question

I’ve got a ‘Knitting in Vogue n2’ book printed in 1984 and I was thinking of doing the cardigan part of a twin set.
It’s a 1958 pattern and calls for the following:
ANI Shetland 2 ply 19x25g
1 pair 3mm needles
1 pair 3.75 needles
The given tension for 10cm is 26 st and 34 rows.

My question, as a beginner, is this: I always thought 2 ply was very fine, good for baby clothes etc. The photo of this cardigan in the book seems to show a more robust wool. Is that because it’s Shetland? Or maybe those ‘ply’ terms have changed over time?

Ply isn’t really a very reliable yarn descrption since the size of the ply can vary. The gauge or tension gives you a better idea of yarn weight and yours is in the sport/baby yarn category.

Check also in the pattern description that the yarn isn’t held double.

Had to uhh we the way back machine, but here’s why ply isn’t helpful.

Thanks for the info. You can see how long I’ve been away from knitting. There was a time ply meant something!

I am also about to knit a 1950s Vogue pattern but this one called for “3 ply” and gave the tension in terms of stitches and rows per inch. I bought a number of yarn samples and made some trial swatches. In the end I chose a 4 ply Alpaca, which seems to as thin as the originally specified 3 ply.