An awfully effective, real-world-based system of weights and measures still used in some countries such as the US and partly in the UK - despite the almost dictatorial pronuniciamentoes of the EU 'Yurp'} that everything must be measured in some - mis-measured - micro-fraction of the Earth's semi-demi-circumference.
Revolves around measuring weight, length, distance and energy etc. in units that actually do make sense - inch - called 'un pouce' in French is the length of the first digit of your thumb; span is the span of a man's hand fingers outstretched; a foot - 'un pied' in French - is - well . . . - the length of a foot; a yard is a pace or step; acre is the area a horse will plough in a day 220yards by 22 yards; a chain - 22 yards - is the length of a cricket pitch. And so on.
Unlike the metric system which may have been taken on board by most countries and is used in - almost - all science - the brightness of nebulae is - please note - measured in crabs and millicrabs; but you knew that.

Seriously, metric works for scienfitc calculations. But - when did you last have to work out the weight of an inch of rain falling on an acre (versus a centimetre of rain on a hectare!).