I keep getting “Least count and instrument reading” questions wrong in Experimental Skills. What's the trap?
adding a positive zero error instead of subtracting it from the observed reading.
The usual trap: adding a positive zero error instead of subtracting it from the observed reading. How to avoid it: correct reading = observed reading - zero error. Go back to the definition — An instrument cannot honestly resolve changes smaller than its least count. A final reading combines the main-scale reading, coinciding-division contribution, and the zero-error correction with correct sign.
Key point
Least count and instrument reading
Common mistake
adding a positive zero error instead of subtracting it from the observed reading.
Memory tip
correct reading = observed reading - zero error.
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