The instruments in chapter 2 are fine for ordinary building, but when the task includes large excavations, or earth moving by machinery, sighting instruments are helpful. The most common sighting task is levelling foundations, but irrigation channels, drainage ditches or pipes, or roof guttering, need to slope at a small gradient for water to flow - how much depends on the application. This chapter covers levelling, ground height difference and slope (gradient) measurement, and instruments for doing so.


To check the level of the ground, or measure the difference in height between two points,, use a level, staff, and target(Also see ‘Accessories’).

Like this:-

a. Set up instrument and stand at one point, and level the instrument, with the sight line pointing at the second point.

b. Stand the staff next to the instrument, and mark the height of the sight line on it.

c. An assistant stands the staff at the second point, and moves a target up or down the staff until the top edge is on the sight line. Mark this point on the staff.

d. The distance between the marks on the staff is the height difference between ground points.

Example:- Height of level sight line :- 1.5 Metres.
Level height mark on staff :- 1.5 Metres.
Height of target on staff :- 1.2 Metres.
Difference in height between level and staff (X) :- 1.5 - 1.2 = 0.3 Metres.
Difference in ground height from level to staff (Y):- 0.3 Metres.



Difference Method. The distance of the measurement can be doubled by sighting both ways; provided the line of sight is truly level, the height of the sight line need not be known. Like this:-


. To find the gradient, G, of a ground slope:-
a. Measure the height difference, H, as above (either method)..
b. Measure the distance, D, between the ground points.
c. Multiply D by 1/H, or just divide D by H. And express G as “1 in D/H”

Numerical example. H = 0.5 M.. D = 2 M.
Then G = D/H = 2/0.5 = 4. Then the gradient is expressed as “1 in 4”.


Adding Sights to an Existing Level. Many builders have a bubble (spirit) level, and sometimes use it for sighting, by mounting or resting it on a stand, and looking along the top edge. But the accuracy is poor; if your eye ts close to one end, that end will appear blurred, and if the colour of the level is similar to what you are looking at, it can be hard to see where the front is pointing.
A big improvement can be made by fitting the level with sights at each end; if the sights are made from hinges (See ‘Open Sights’ in ‘Instrument Parts’), they can be folded down, and won’t take up any more room in the toolbox. Because levels differ in construction, detailed instructions can’t be given. But a few comments may help.

An I-beam level is good for fitting sights, because they can fold down inside the beam. Hinged sights can be mounted on small wooden plates, screwed to the frame at each end. Put another block roughly in the middle, with a hole for mounting the level on a stand. This block should be thick enough for the surface to be flush with the edges.

With a box level, it may be possible to mount the sights directly on the beam, but be careful where you drill holes; leave plenty of clearance around the bubble indicators, because you can’t see how far they extend inside. A mounting hole allows the level to be screwed to a stand.



Left :- A 600 mm. commercial bubble level fitted with folding sights and a mounting block. The level is clamped to the stand with a 6 mm.(1/4 “) eyebolt. The wing nut shown on the eyebolt has since been replaced by a T nut set in the mounting block.
The sight vanes have V notches cut in the side to help locate the target. Each guy rope has a toggle to help set the stand vertical. Making open sights suitable for a level has been shown in ‘Instrument Parts’..

Aligning bidirectional sights can be done with an end for end check. Each sight should first be held in place only by one central mounting screw. The sights will be easier to see through if painted flat black.

1. Set up the instrument facing a sheet of blank paper, 3 to 5 metres away; the paper should be well lit. Set the instrument level.

2. Look at the paper through the sights, with an assistant to mark the paper in line with the foresight notch. For sights fitted with shutter bars, look at the paper with the fore sight open and the back sight closed to a slit. If you are doing it on your own, use a vertical scale target (see ‘Accessories’), and record the number in line with the sight line. Like this:-


3. Turn the level around the other way, reverse the shutter bars if used, and repeat step 2, making a second mark on the paper (or note the target scale number).
4. Put a heavy mark exactly half way between the first to marks (or locate the half way number on the scale). Then without moving the level, gently tap the back sight up or down until the the third mark and the foresight are in line. If the back sight can’t be lined up without knocking it too far out of square, try tapping the foresight a little each way.

5. Repeat steps 1 to 5 until the sights are in line in both directions. Then put screws in the other two mounting holes of each sight.


The sights are now ready for use.


An Improvised Self Adjusting Dumpy Level. This instrument is easy to make, floats in water in a suitable container, and gives a level sight in any direction without adjustment. Provided an alignment check is carried out, this device gives quite good results. -
The water container should be from 200 mm. to 300 mm. diameter. . A shallow container (e.g. biscuit tin, flower pot saucer, old frying pan) is deep enough, and is easy to raise to eye height. A deep container (e.g. paint can, bucket, oil drum ), being heavy, is good in the wind.
Make the float from a board 150 to 200 mm. wide, and curve the ends so that it floats in the water container, with a small clearance between the ends and the container wall. The backsight is made from thin sheet metal as described in “Open Sights” (See “Instrument Parts”); except that the V notch is cut in the side of the vane. Like this:-



The accuracy of the level depends on getting the centre line of the notch exactly horizontal, so cut out the template below, and stick it on sheet metal. Then cut out the vane, V-notch, and shutter with tin snips, using the template as a guide. Keep the template to colour the backsight black. Like this:-


The crosshair is nylon sewing thread or fine fishing line, at the same height as the backsight notch, about 13 - 14 mm. above the float deck. Colour the crosshair black for about 10 mm. in the middle, to help see it against white backgrounds.
The balance weight can be any small, heavy object which can be screwed to the deck - a 12 mm.(1/2 inch) nut, or fishing sinker drilled for a screw. DO NOT screw the balance weight in position until aligning the level (see below).
Another way to make a backsight is to saw a slit across the base of a small tin can with a junior hacksaw, and fasten the can in position with a pipe saddle, or a saddle made from a larger diameter but shorter can - leave the rolled edges in place for strength. The can provides shade for the slit, and can be turned to bring the slit parallel with the float deck and foresight.
Secondly, the foresight can be made from a strip of strapping iron (see ‘Instrument Parts’), held in place by two 6 mm. machine screws and 6 nuts (see below).

Setting up the Improvised Level. 1. Look at the crosshair through the backsight; it may look blurred. Move your eye closer to the tip of the notch until the crosshair looks sharp, and close the shutter blade to cover the wide end of the notch.
2. Fill the container and roughly level it, using the water surface as a guide. Gently place the level in the water - some may spill; it should spin freely without touching the sides, but may not be floating level. Place the balance weight, and its fastening screw, on the centre line, and roughly balance the float by moving the weight backwards and forwards along this line. Do not screw it in place yet.
3. Hang up a blank sheet of paper 3 to 7 metres in front of the level, and look at the paper through the backsight. Make a faint pencil mark in line with the centre of the crosshair.

4. Open the shutter bar, turn the float half way round (don’t spill water), and look through the sight and crosshair back to front. Move your eye until the crosshair and notch tip are in line. If the crosshair appears blurred, stand back a little, or look through a pinhole pricked in a piece of cardboard. Now mark the paper in line with the notch and crosshair. You should now have two lines on the paper, one above the other.

5. Put a heavy pencil mark half way between the first two. Again gently turn the float round, close the shutter bar, and move the balance weight backwards and forwards until the centre of the crosshair is on the third mark. Like this :-


6. Check that both ends of the crosshair are also in line with the third mark. If not, move the balance weight from side to side until they are.
7. Repeat steps 3 to 6 until the float is level both forward and back, and from side to side. Then screw the balance weight in place.
The level is now ready for use. Always move the level gently so as not to spill water, and if you are using it in one position for more than a day, put a reference mark on a nearby fixed object and check the level against it every morning. Then make up any water losses.
If the level swings in the wind, put a little sawdust in the water. If it bobs up and down, steady it with a finger, but let go before taking a reading - touching the float when looking through the sights will unbalance it. If you must steady yourself, hold the water container or its stand. Anything added to or taken away from the float upsets the balance, so make all changes before doing the end for end check.


Two ways of making an improvised dumpy level.

Left. As described in the text It uses a frying pan minus handle as the water container.
Lower. Sized to fit a bucket, it has a slit tin can backsight, and a strap iron foresight. 0.8 mm. thick. which obscures more of the target than a nylon foresight. But it is possible with practice to sight off the top edge of the strap iron, and as this is hard to damage, it is recommended.




Part 4 shows two advanced dumpy levels.