[jdietrich]

It's only a problem in the US. The Commonwealth ton is only 1.6% larger than the tonne, so the distinction is usually insignificant. Most of the world has no knowledge of either the short or long ton.

Likewise, confusion between "mills" (millimetres) and "mils" (thousandths of an inch) are an exclusively American problem.

The American adherence to customary units is a constant annoyance for electronics engineers - an 0603 resistor could measure 0.6mm x 0.3mm or ~1.5mm x ~0.76mm

[tonyarkles]

Sadly also a Canadian problem. We're nominally a metric country, but we're very much a hybrid. When we went to metric, many things still stayed in customary units, but with metric names. I'll likely never ask someone to go get me 454g of sugar from the grocery store, it'll be a pound. Your 2x4 is going to be 8 feet long. You're going to use 1/2" bolts. My generation does consistently use litres and celsius though!

[sokoloff]

I think the SMD resistors are well standardized.

A resistor measuring ~0.6mm x 0.3mm is an 0201. (2 1/100ths of an inch by 1 1/100th of an inch.) The standard doesn't make sense in SI units, but it's the standard.

[jdietrich]

SMD passives are listed in both metric and imperial units. Most sizes are unambiguous, but 0402 and 0603 resistors exist in both series. There's also possibility for confusion between the imperial 01005 and the metric 1005. These parts are specified in metric, making the imperial sizes purely nominal.

http://www.newark.com/chip-smd-resistors/resistor-case-style...

The metric/imperial split is a constant nuisance. Most board houses and PTH packages use mils, but the vast majority of SMT IC packages are specified in millimetres. Board layouts almost always necessitate switching between imperial and metric units; Layout software includes features to manage this. Wire gauges are a total mess - AWG, SWG and mm are all in common use. Standard pin headers and derivative connectors are 0.1" pitch (2.54mm), but JST connectors are 2.5mm pitch. Conversion errors have caused countless production problems.

[MatthewWilkes]

Mils really confused me when I was learning PCB design. In the UK a thousandth of an inch is not a common unit anymore, but it isn't unknown. The problem is that we call it a "thou".