New Digital Scale

[Nusa]

But, the weight of coins could be useful in some circumstances when 1% is "good enough for Australia".

But scales most likely will be better than that even considering they were calibrated at place with different gravitational acceleration. So IMHO the most you can use them for is checking if scales are not displaying outright wrong numbers. Or making a rough calibration on scales which were calibrated a very long time ago and thus drifted over time.

I was thinking of rather extreme circumstance, e.g. you are camping, don't have a scale with you, and need to measure out an ounce of butter...   and you do have five quarters!

Out of curiosity, how do you use the quarters if you don't have a scale with you?

As far as butter goes, there's usually 4 sticks in a pound, so 4 oz per stick, so 1 oz would be 1/4th stick. And that information is generally marked on the stick wrapper as well. Alternately, you could just remember two tablespoons in an ounce. I'm aware that "ounce" is an ambiguous unit. For cooking purposes while camping, the weight and volume measures are close enough to the same thing in the case of butter. (Of course, real cooks are experienced enough to eyeball such things, even when the tools are available.)

I can see, I should have put a smiley in there somewhere! 

OK so in the hypothetical situation where you need to weigh something to 1% and you don't have a scale, but you do have 6 quarters:  you could make a makeshift balance out of random materials that you find, and balance it using three quarters on each side, before using the quarters for weighing the target material?

But if you make a scale, then you DO have a scale with you! The extreme circumstance only applies if you DON'T have one.

[JohnnyMalaria]

Calibrate it with a known volume of water. Got an old syringe or maybe a measuring cup from a cough medicine bottle? Good enough for cooking.

See attached. Water filled to 25mL mark by eye and weighed on my analytical balance.

[SilverSolder]

It's easy enough to make a balance or a scale...  much harder to calibrate it! 

[beanflying]

Depends on the accuracy you need or if you are building something from scratch then having a set makes testing linearity really easy.

I brought this set of calibration weights a year or so back for about $20. Interestingly they compare very well with the two 50g weights that came with my 100g cheap and cheerful scale I brought 7 or 8 years ago. No reason the cheap cal weights on evilbay won't be close and you can always cross check them against one known which I did initially with my set. I have used these smaller sets to check the larger digital scales I use for coffee roasting by filling small cups to a known 100g against them. Uncertainty  but a lot better than I need in particular when I cook