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The term tachometer is borrowed from the Greek language. With tachos for fast and metron for measuring device, the tachometer thus also stands in the original meaning for a speed measuring device. Compact device models, which are held in the hand during the measurement, are called handheld tachometers in contrast to permanently installed models. The offered models differ mainly by the measuring range, the measuring principle and the additional functions. In order to find a suitable handheld tachometer for the intended application, the most important requirements for the device should be determined in advance.
Handheld tachometers for control measurements during maintenance and repair work 
usually measure the rotational speed in revolutions per minute. The unit is displayed as rpm or RPM. RPM is the English abbreviation for "rounds per minute". Occasionally, the rotational frequency is also indicated in hertz. One hertz corresponds to one revolution per second and 60 revolutions per minute.
The measuring range is usually limited by the design of the instrument to the following values:
Not all handheld tachometers can completely cover these value ranges. Therefore, when selecting an instrument, it is essential to ensure that the measuring range covers all the required speeds.
The rotational speed can be determined mechanically, optically or stroboscopically with the handheld tachometer. Some models allow measurements with two or even all three measuring principles. Make sure that you select the handheld tachometer that is suitable for your tasks and operating conditions. If only the rotational speed or rotational velocity is to be determined, all three methods are applicable.
However, the handheld tachometer that works via contact must be able to be placed directly on the measuring point. For the models that measure optical reflections, the distances between 5 and 50 cm are sufficient, with some instruments even up to 1.5 meters. If the surface speeds or line lengths on rollers or conveyor belts are to be tested, the handheld tachometers with contact measurement are particularly suitable. The rotations of the measuring wheel can be easily converted into line speeds and lengths.
The handheld tachometers for contact measurement are often supplied with various attachments. The measuring wheels and measuring tips enable the synchronous transmission of the movement of different components to the shaft of the measuring instrument. A measuring wheel can also be used to determine the running speed of rollers, grinding belts or conveyor belts. To do this, the handheld tachometer multiplies the rotational speed in revolutions per minute or second by the circumference of the measuring wheel. Some handheld tachometers of this type, for example the analogue versions with dial scales, are also suitable for applications in hazardous areas.
The optically reflective measurement also works without touching the component to be 
measured. The handheld tachometer emits radiation for this purpose and evaluates the reflections. In most cases, the targeted position can be checked with the aid of a visible laser aiming point. In order for the revolutions to be recorded correctly, only a small part of the rotating surface should reflect the radiation well. For this purpose, a mark made of special reflective tape or reflective paint is applied close to the outer diameter of the component. When measuring, the handheld tachometer uses a light-sensitive sensor to detect the reflected radiation and then evaluates the time interval between the reflections.
In the stroboscope effect, the timed flashes of light illuminate objects only briefly. Rotating objects appear to be stationary if their rotational speed matches the frequency of the light flashes. Then the object is always in the same position when it is illuminated. For correct evaluation, an optical marking is required, for example in the form of a clear label, notch, groove or hole.
If a component rotates several times between two light flashes, this cannot be distinguished optically from a single rotation. Many handheld tachometers therefore have function keys with which the light cycle can be increased or decreased via multipliers so that the rotational speed is determined correctly. However, stroboscopes as handheld tachometers allow not only the determination of rotational speed and rotation rate. They can also be used to slow down fast movements to slow motion speed and thus make the irregularities visible.
Many handheld tachometers can store the minimum and maximum rotational speed of the current series of measurements. In certain types of instruments, the average value is also calculated. For the users where the use of different units is common, the instruments where the unit can be changed simply by pressing a button are recommended.
Handheld tachometers with additional sensors, e.g. for temperature or vibration measurement, are ideal when the repairs, maintenance or servicing have to be carried out on machines that are difficult to access. In addition to the speed values, additional vibration and temperature data can then be recorded immediately with the same device.
If the measurement data is to be logged or evaluated after the measurement, it is advisable to select the handheld tachometer with a sufficiently large and convenient memory. Then the values do not have to be recorded additionally in lists or tables on site. The data can be retrieved later or, if the handheld tachometer is equipped with a data interface, simply read out.
Tachometers as many other measuring instruments have been significantly developed over 
the last years and are nowadays presented by compact digital devices capable of carrying out the measurements reliably and quickly. The name of the device speaks for itself, due to its Greek origin, and it is clear that its main task and function is connected with the speed measurement. It goes about various speed measurements, and it applies especially to industrial branch, where the rotating details and mechanisms can be found in abundance. It should be, though, noted that speed measurement is just one of the applications of the modern digital tachometers.
Panel tachometer works not only in the mode for the determination of speed, at which certain parts in the machine are moving / rotating, but also for determination of the number of pulses per revolution, with the timer function or even chronometer, which means that modern digital industrial tachometer is not limited to only pure speed measurement and it makes it applicable in many situations, for example, in all possible types of vehicles, aviation, for maintenance checks, testing of the equipment, counting of the produced items on the conveyor belt, or control and assessment of the consumption of the materials. The latter is realized due to the function of pulses counting and is especially helpful at the enterprises working with the flow of goods on the conveyor belt. Significant raw material saving can be achieved if the control is carried out with the help of the reliable industrial tachometer, since by determining the number of pulses, it detects overconsumption or wrong distribution of the goods on the belt, which leads to descend in the production.
Tachometers helps to assess the productivity and performance of various mechanisms, rotors, 
engines. It is important in order either to sustain the work on the existing level, or to be able to introduce certain changes so that to provide the best conditions for the machines with the rotating parts and thus prolong their service life and improve the performance of the production process. The quality of the output product may also be improved due to the integration of the panel tachometer for continuous monitoring. Selection of the correct working parameters within the permissible range helps to ensure the best working conditions, and tachometer installed on the dash panel is an important link in the chain of the controlling equipment.