Instruments used in Levelling

The Automatic Level

1. Gun sight
2. Circular level (pond bubble)
3. Levelling Screw
4. Base Plate
5. Objective Lens
6. Focusing Knob
7. Horizontal fine motion screw
8. Horizontal circle window
9. Horizontal circle setting ring
10. Reticle adjusting screw cover
11. Eyepiece

Setting Up an Automatic Level

1. Set up the tripod at just above chest height. Make sure it is stable, and mount the level on the top.
2. Adjust the leveling screws until the pond bubble is centralised.
3. As long as the pond bubble is central, the automatic compensators are able to finely level the instrument. To ensure this is the case, whilst looking through the scope, gently tap the level. The view will waver for a few moments before steadying. If this does not happen, the instrument is not level enough for the compensators to cope, and needs adjustment.

Sighting

1. Sight towards the staff using the gun sight.
2. Look through the eyepiece and focus the reticle by gradually turning the reticle focusing ring anti-clockwise.
3. Turn the focusing knob to focus on the staff.
4. Turn the fine motion screw to centre the staff in the field of view. Turn the focusing knob to eliminate parallax between the staff and reticle.

The Levelling Staff

Reading the Staff

The staff starts at zero, on the ground. Every 10 cm is a number, showing ( in meters to one decimal) the height of the bottom of what appears to be a stylised E (even numbers) or 3 (odd numbers), 5 cm high. The stems of the E or 3 and the gaps between then are each 10mm high. These 10mm increments contiunue up to the next 10cm mark.

To read the staff, take the number shown below the reticle. Count the number of whole 10mm increments between the whole number and the reticle. Then estimate the number of mm between the last whole 10mm block and the centre of the reticle. The diagram above shows 4 readings:- 1.950, 2.000, 2.035 and 2.087.

The person holding the staff should endeavour to hold it as straight as possible. The leveller can easily see if it is tilted to the left or right, and should corect the staff-holder. However, it cannot easily be seen that the staff is tilted towards or away from the leveller. In order to combat this possible source of error, the staff should be slowly rocked towards and away from the leveller. When viewing the staff, the reading will thus vary between a high and low point. The correct reading is the lowest value.

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