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It's how literally all engineering in this country was done a single generation ago. When I studied mechanical engineering it was all units like slugs and foot-pound-second.

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> A slug is defined as the mass that is accelerated by 1 ft/s2 when a net force of one pound (lbf) is exerted on it.[2] One slug is a mass equal to 32.1740 lb

this is like if you tried to explain the difference between a newton and a kilogram to an alien an they didn't quite get it

It's not that complicated. A slug is the Imperial unit of mass, like the kilogram. It's just that while in metric the unit of mass is primary and the unit of force (Newton) is derived, in foot-pound-second it is the reverse. Pounds is a fundamental unit of force and the slug is derived.

Pound force is the unit for force. Pound mass is the unit for mass. Colloquially people say pound.for both of them

This is true colloquially. In engineering (or at least aerospace engineering, which is what I was studying) we more generally used slugs for mass in our calculations. Gravity/weight isn’t always constant after all, even on earth.

Not universally. We still talked about a rocket’s “pounds of thrust.” But for things like angular momentum, center of gravity, etc. those were usually calculated with slugs.

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