well, considering i was sitting in the bathroom looking at my phone while wearing clothes when i saw your response, i'd say string and a calculator were both equally close at hand.

only one of those can be used as a measuring tool, though... I guess you could mark off how many calculator lengths something is and measure it later. ngl, i hung a shelf using that technique once, but i wouldn't use it to find one third of a length. the nice thing about string is that if you don't have a measuring stick you can always stuff it in your pocket and measure it later when the appropriate tool is at hand.

apologies for any confusion about checking measurements, i wasn't referring to using my own foot to verify the length of a line, but the common practice of using fractional mathematics to make and verify calculations thousands of years ago and to this very day. we have records of this method being used across language and unit barriers in the ancient world.

there's another post earlier itt blaming the mars climate orbiter failure on sae unit conversion but nasa puts the blame on itself for not double checking the software and measurements they got back from lockheed. I remember back in the day hearing about that failure on the news and seeing how it was not a problem of difficulty of conversion between the compound units involved, but failure to actually convert between them at all!

since you brought up calculators, there's a salient point to be made here using a long winded anecdote: when i was in school there was a point in time when suddenly teachers began providing calculators for the exams. this wasn't that magic moment when the mathematics became just too complicated to expect a middle schooler to do it all on paper. last years class had to use longhand, this years class were provided little blue texas instruments scientific units with a ten digit display and helpful guide to performing logs and other operations that would have been taught using super and subscripts glued to the inside of the cover that would be taken back up at the end of the test.

this didn't happen going from one grade level to another, but right smack dab in the middle of the academic year. a whole classroom of students yanked bodily into the digital age.

when the parents found out you'd think the questions were gonna be written on the proctors inner thigh. "i had to do it by hand, my kid should too!" "you're supposed to be teaching them math, not how to use a calculator!" and it's sister "you're supposed to be testing their ability to do math, not use a calculator!" but the most common one by far was "they'll all just get the right answers and we won't know who studied and learned."

when the grades came in there was almost no change from last years class.

there were some individual students who did better or worse than their test history would suggest and a whole bunch of new common wrong answers, but by and large aside from errors the ability to perform calculations in response to a prompt was unaffected by ten signed digits of precision.

how could it be that a calculator made no difference?

it turns out that understanding what a question was asking for, verifying ones work and recognizing wrong answers that needed to be rechecked couldn't be performed by the little blue rectangles.

and many years (and measurements) later i have the same outlook about metrology: comprehension of the goal of a measurement gives you a much better chance to get it right than a calculator.