In this article, we talk about a simple guide on cathetometer. A cathetometer measures vertical distances in liquid surfaces.

A cathetometer is a type of instrument mainly used for measuring variations of a minute in the level related to liquid surfaces with a high degree of precision and accuracy. This article will discuss a simple guide on a cathetometer, its uses, and its operation.

Definition of Cathetometer

A digital cathetometer is a type of instrument mainly used to measure vertical distances in cases where we cannot place a scale at points close to each other, for example, to measure the distance between the mercury levels in a tube.

Working of a Cathetometer

To move an instrument upward and downward in the vertical column for measuring the levels, the horizontal telescope is put on the vertical column to move up and down through the vertical column. Moreover, a cathetometer also uses a type of scale specially designed to read the specific location of the telescope. Therefore, preliminary measurements of a digital cathetometer are taken to read the precise location of the telescope. A primary measurement must be taken to ensure that the cathetometer is at its level when using the cathetometer. After that, the cross-hair in the eyepiece of the telescope should be appropriately adjusted to coincide with the image of another point so that another reading is taken. Thus, the difference between the two readings is correctly calculated as this difference is essential to determine the variations among surface levels.

Functional Requirements of a Cathetometer

The minimum focus distance of the telescope should not be more than one metre.

The linear bubble of the telescope containing the sensitivity should not be less than 30 seconds per 2 mm. The sensitivity of the circular bottle is attached to that of the base.

The least count for the vernier should be approximately 0.01 mm for a 500 mm effective range and 0.02 mm for a 1000 mm effective range.

The carriage carrying telescope should have a proper fine tilting adjustment to understand the line of sight in a horizontal position.

The sensitive level of a digital cathetometer’s telescope should be provided to make the line of sight horizontal.

The optical axis of a telescope is generally within 60 mm of the plane of scale.

Moreover, the parts of the cathetometer column should form the guideways for the carriage and be straight along the length for one minute of arc.

Along with these, there are few other functional requirements of a cathetometer.

Materials as per Guidelines Required to Build a Cathetometer

As per guidelines, the vertical and vernier scales shall be made out of a material that is corrosion resistant, which must have a coefficient for a linear expansion that should be not greater than a 0.000 020 per degree Celsius.

The material of the optical components of the cathetometer should be in accordance with that of ISO standards.

The material for the bubble should also conform to the ISO standards.

The material for the other components of the cathetometers should be strong and of good quality.

Following is a diagram of a cathetometer.

Operating Procedure of a Cathetometer

First, attach a proper cathetometer to a height gauge.

Now place the height gauge on the surface plate or any other surface which is flat.

Try to look through the eyepiece and turn the knurled knob with the eyepiece until the cross-hair comes into a sharp focus.

Then try to adjust the height of the cathetometer accordingly until the object is at a sharp focus.

Try to readjust the height with that of fine adjustment to bring the starting point in line with that of the cross-hair for the cathetometer. The adjustment on the cathetometer can also be used for levelling the instrument if it possesses its own liquid level.

When the cathetometer is linked with the starting point, the technician then takes a vernier reading on the beam of the height gauge. The cathetometer can be used on the vertical beam for the height gauge to the next point. Thereafter, the technician takes the reading and subtracts the first reading from that of the second reading. The distance between the two points can thus be measured.

One can also take further readings with the same procedure as mentioned above.


Cathetometer is used for various purposes, but its main use is in reading the levels of a liquid in a capillary tube for measuring the surface tension. Moreover, a cathetometer is often employed for determining the changes in the liquid level during a chemical reaction.