On Sat, 17 Feb 2018 11:53:34 -0800 (PST), wrote
in

What does 10w30 mean on oil cans? Is it 10 winter and 30 what? And how is it determined?

The viscosity of the oil at operating temps is 10, but it's
lubricating effectiveness is 30.
--
Web based forums are like subscribing to 10 different newspapers
and having to visit 10 different news stands to pickup each one.
Email list-server groups and USENET are like having all of those
newspapers delivered to your door every morning.