> but projects invariably consist of many people and each of them "think" in their unit of measure.

Obviously, you'd assemble project teams who are familiar with the tools, techniques, and conventions that you intend to use with your project.

> Sure you can mix them and hope they remember to "think" in metric at 1AM when pushing for a deadline, but really...

And the Chinese engineer who's working on a project where all of the documentation is in English might slip up when he's punchy at 1 AM and accidentally complete some of his work in Chinese.

This is a good argument for making sure that team members are well-rested and alert while doing their work. It's also a good argument for scheduling work reviews, proofreading, and time for correcting errors in the project plan. It's not at all an argument for abolishing the Chinese language.

> Thats the thing. These are not tools. They are units of measure.

Units of measures are tools. Tools are devices, whether physical or conceptual, that we use to extend our capacities for interacting with the world. In this case, since human beings do not natively have the capacity to quantify continuities, we apply the tool of measuring units to break continuities down into discretely countable chunks.

And, like all tools, how well they work depends on what goals you're trying to accomplish, and in what order of priority, in a given set of circumstances. Metric units are great in a limited set of contexts in which uniformity of post-hoc representation is more important than practicality in the activity of measurement itself; but this means that they are, for the same reason, less effective than customary units for the vast majority of situations that involve measurement.

> Definitely. Eyeballing happens regardless of unit of measure. And usually when someone is eyeballing it its not life/death.

Very few situations are matters of life and death, and in those rare circumstances that are, people will naturally be cautious and rigorous in their methods: I'd expect people to use precise measuring instruments, and to perform measurements multiple times, so in such a situation, questions of familiarity with particular units are scarcely relevant. When you're relying on the precision of instruments, the actual measuring units you're using are less important: metric, imperial, or otherwise, they'll all work just as well.

> Units of measure is something thats internalized from a high-school age

I don't know how much anyone "internalizes" any measuring units, but to the extent that they familiarize themselves with theDefinitely. Eyeballing happens regardless of unit of measure. And usually when someone is eyeballing it its not life/death.m, there's certainly no cause to familiarize oneself with only one set, at the exclusion of another.

> So unless you have a way of splitting the kids between space engineers and carpenters at that age then why tech imperial?

How about we keep doing things the way we are - teaching everyone both sets of units - and letting them determine for themselves which ones are most useful to them for each particular application?

> I get that Americans are attached to imperial...its just very difficult for everyone else to under why given this: http://i.imgur.com/YJzhkZl.jpg

All that graphic demonstrates to me is that while, with imperial/customary measures, there are a variety of separate base units to choose from, each appropriate to a particular scale of operation, the metric system only offers one base unit, and pretends that applying a 10^x coefficient to that single base unit somehow makes it a different unit.

That's what you're not getting: feet, yards, inches, etc. are fundamentally distinct units that have been tweaked to relate to each other, where necessary, by factors that are often much more convenient than 10. But you're just as capable with customary units as with metric of sticking with a single unit and applying scaling factors: I can just as easily say e.g. 24.2 x 10^4 feet as 45.83 miles.

I can even use metric prefixes if I'm so inclined, and say 24.2 kilofeet! Or 2.9 megainches! All the same value. But using these prefixes is just a bizarre re-implementation of scientific notation: in what way does it make sense to encode quantitative information as a verbal prefix appended to the name of the thing you're counting, instead of just using numbers?