18-09-2019, 01:04 PM
(18-09-2019, 06:36 AM)Amie Wrote: Dad used to say not to worry about too many decimal places, he said that one of his tutors took his very expensive new calculator away from him (late 1970's) and gave him a little six inch slide rule, telling him it would be as accurate as he would ever need for in electronics! (Boots ringplan, I still treasure it).
Largely true, but you do need to be careful.
I quite often measure power going into (volts x amps) and out of (different volts x different amps) a transformer. usually the powers are nearly equal; subtracting them gives the losses in the transformer.
When you subtract two nearly-equal numbers, a small change in either can make a massive change to the answer. Example, 990W out, 1000W in, so 10W lost. But make a 1% uncertainty in input power (which is about the limit of a slide rule), thus I may be from 990W to 1010W in, and the losses could be from zero to 20W, a +/- 100% change! And this could mean the difference between needing a fan to cool it, or not needing a fan.
Accurate calculators are great, and I have access to as many figures of accuracy as I need, which wouldn't be the case with a slide-rule. (Though, I still know how to work out with pencil and paper)!
