As a former mechanical engineer, any calculations involving pounds in any form I pretty much always converted to metric and then back at the end if need-be. The trinity of pound-mass, pound-force, and slugs is incredibly easy to screw up--at least as a student.
Admittedly, engineers are pretty much the only people making calculations with those kind of units and they generally use metric as far as I know. I went to school a long time ago and there were probably enough legacy imperial units hanging around that it seemed worthwhile to at least be exposed to examples you wouldn't have encountered in day to day living.
Since the 60s, America has literally been officially a conversion of standard SI units. A yard is defined as most of a meter (exactly 0.9144 meters) and an inch is derived from that.
Since the 60s? The yard measurement dates to sometime before the Norman invasion of England. And it's not even used that widely in the US outside of some specific contexts like sports. A gallon, from which a quart is derived is of a similar vintage. Without digging into history, I assume some SI volume and length measurements roughly mirrored existing Imperial units as opposed to the other way round.
The point is that the American units are now defined relative to metric units.
As recently as the 1800s, the yard was defined as:
"the Straight Line or Distance between the Centres of the Two Points in the Gold Studs of the Straight Brass Rod now in the Custody of the Clerk of the House of Commons whereon the Words and Figures "Standard Yard 1760" are engraved"
... That standard yard was destroyed in a fire in 1834, and a new standard yard was made using several copies of the original standard yard as reference.
But now, it's just defined as an exact fraction of a meter. First as 36/39.370113 m, now as exactly 0.9144 meters.
