Question

If the sensitivity of bubble tube of a levelling instrument is 30" per 2 mm division, then the error in the staff reading on a staff held at a distance of 80 m caused by the bubble being 2 divisions out of the centre, will be

• A. $3.02cm$
• B. $1.16cm$
• C. $2.84cm$
• D. $1.58cm$

Answer 1

The correct option is B $1.16cm$

$\alpha =\frac{\left(s\right)}{\left(n\right)D}\times 206265"[\alpha =\frac{30"}{2}]$

$\Rightarrow 15=\frac{s}{2\times 80}\times 206265"$

$\Rightarrow s=0.0116m$

$\simeq 1.16cm$