What if you get a new ruler that’s 4 times as precise than the one you have that measures to 0.1cm? You don’t want to record it as 0.70cm, because that’s more precise than your measurement. But you could record it in 40ths with fractions.
Another way to look at it is that decimal is already a fractional system (1/10, 1/100, 1/1000) that doesn’t allow you to use 90% of possible fractions.
If there’s a technical need you can have your scale divided into whatever you want. There’s nothing preventing you into dividing your scale every 0.25mm to get 1/4th precision. It’s very rarely done because there’s no need, but it’s absolutely possible.
Thermometers have sometimes division per 0.5°C instead of 1°C
Yes, but how do you record that precision without needing a qualifying statement. When precision matters, “0.25” represents a measurement that is known to be closer to 0.25 than it is to either 0.24 or 0.26. Something that is only precise to 1/4 of a unit isn’t that precise. The decimal way to record a precision of 1/4 is “0.25 +/- 0.125”.
The thing to understand about decimals and precision is that you’re still recording a fractional measurement, but your denominator is fixed to powers of 10. 0.1 is 1/10. 0.01 is 1/100. So when increasing precision by less than a factor of 10 is difficult to represent.
This matters a lot for things like digital calipers, where a cheap set will show the same measurement as a nice set that’s more precise because the good ones aren’t 10 times as precise. But if they have a fractional setting, the nicer ones will read more precisely because that increased precision can be represented on the display.
What if you get a new ruler that’s 4 times as precise than the one you have that measures to 0.1cm? You don’t want to record it as 0.70cm, because that’s more precise than your measurement. But you could record it in 40ths with fractions.
Another way to look at it is that decimal is already a fractional system (1/10, 1/100, 1/1000) that doesn’t allow you to use 90% of possible fractions.
If there’s a technical need you can have your scale divided into whatever you want. There’s nothing preventing you into dividing your scale every 0.25mm to get 1/4th precision. It’s very rarely done because there’s no need, but it’s absolutely possible.
Thermometers have sometimes division per 0.5°C instead of 1°C
Yes, but how do you record that precision without needing a qualifying statement. When precision matters, “0.25” represents a measurement that is known to be closer to 0.25 than it is to either 0.24 or 0.26. Something that is only precise to 1/4 of a unit isn’t that precise. The decimal way to record a precision of 1/4 is “0.25 +/- 0.125”.
The thing to understand about decimals and precision is that you’re still recording a fractional measurement, but your denominator is fixed to powers of 10. 0.1 is 1/10. 0.01 is 1/100. So when increasing precision by less than a factor of 10 is difficult to represent.
This matters a lot for things like digital calipers, where a cheap set will show the same measurement as a nice set that’s more precise because the good ones aren’t 10 times as precise. But if they have a fractional setting, the nicer ones will read more precisely because that increased precision can be represented on the display.