Topic 11: Least Count of Measuring Instruments

<h2>What is Least Count?</h2>
<p>
The <strong>least count</strong> of a measuring instrument is the smallest
measurement that can be accurately measured using that instrument.
It represents the precision of the instrument.
</p>

<h2>Importance of Least Count</h2>
<ul>
  <li>Determines accuracy of measurement</li>
  <li>Smaller least count → higher precision</li>
  <li>Very important for experimental and numerical questions</li>
</ul>

<h2>Least Count of Common Instruments</h2>

<h3>1. Meter Scale</h3>
<p>
Least Count = <strong>1 mm = 0.1 cm</strong>
</p>

<h3>2. Vernier Calipers</h3>
<p>
Least Count = <strong>Value of 1 Main Scale Division − Value of 1 Vernier Scale Division</strong>
</p>

<h3>3. Screw Gauge</h3>
<p>
Least Count = <strong>Pitch / Number of divisions on circular scale</strong>
</p>

<h2>Why Least Count Matters</h2>
<p>
Even if a measurement looks correct, the least count limits how accurately
it can be reported. No measurement can be more precise than the least count
of the instrument used.
</p>

Least Count – Quick Revision

Definition

Least count is the smallest value that can be measured accurately by an instrument.

Formulae

• Meter Scale → LC = 1 mm
• Vernier Calipers → LC = 1 MSD − 1 VSD
• Screw Gauge → LC = Pitch / Circular divisions

Exam Tips

• Always write unit with least count
• Used directly in numerical problems
• Often combined with zero error questions