Among the given options, the correct one is:
C) Correction = + [ln - coinciding divisions C.SI × L.C]
Here's the explanation:
When using a screw gauge, the zero error refers to the error that occurs when the two measuring faces of the screw gauge do not perfectly coincide when there is no object being measured. A negative zero error means that the '0' marking on the circular scale is below the reference line or the '0' marking on the main scale.
To correct this negative zero error, we need to add a positive correction to the observed measurement. The positive correction helps to bring the '0' of the circular scale to the reference line.
In the provided option C, the correction is mentioned as "+ [ln - coinciding divisions C.SI × L.C]." Let's break down this expression:
"ln" represents the least count of the screw gauge (i.e., the smallest measurement it can make).
"coinciding divisions C.SI" refers to the number of divisions on the circular scale that coincide with a reference line when there is no object being measured. Since the zero error is negative, these divisions will be below the reference line.
"L.C" represents the length of one division on the circular scale.
So, adding the positive correction "[ln + coinciding divisions C.SI × L.C]" to the measured value will correct the negative zero error.
