To make the UoS visible in "Product/Sales" you have to check "Allow Use of secondary unit of measure" in the user preferences.

The best (fool proof) way which also works on POS is described here: https://www.twanda.ch/en_US/slides/slide/wine-by-the-glass-3

Use cases of Unit of Sales (UoS):

Case 1: The UoS can be used when you sell in different quantities of the standard UoM but of the same category. For example if you stock grain in tons but sell it in kg.

Case 2: If you stock in units but sell for example in kg, but only if the stockkeeping unit is consumed completely by the sale. Example: You stock chicken in units, but you want to sell them by their individual weight at a price per kg.

This is the link to the presentation glass by wine, that worked for me:

https://www.twanda.ch/en_US/slides/slide/wine-by-the-glass-3 (only in firefox, not in safari or chrome) Seems to load for a long time.

The embedded file is at https://www.twanda.ch/en_US/slides/embed/3?page=1