Making measurements with Searle's apparatus

We have been using Searle's apparatus to gather data that we will use to find the Young Modulus for steel wire. It is the same sort of scale as on a micrometer screw gauge. The vertical scale on the left hand side is measured in mm from 0mm to 10mm. One complete turn of the central barrel moves the leveling apparatus by 0.50mm. You start by taking a reading on the left hand vertical scales using the top of the rotating barrel as your marker. The problem is that it takes two complete rotations to move the 1mm between scale divisions on the vertical scale. So you have to make a decision about whether you are below or above 5.5mm for the situation shown in the picture.I think we are below, so we take 5.0mm and add the reading from the barrel, taken where it meets the vertical scale. It is 36 to the nearest whole number. Hence the reading is 5.0 + 0.36 = 5.36mm.