1mm plus 1ppm is the abbreviation of 1mm plus 1ppm×D (kilometer), which reflects the nominal ranging accuracy of the total station or rangefinder.

Among them: 1mm represents the fixed error of the instrument, which is mainly caused by the measurement error, centering error, and phase measurement error of the instrument plus constant. The fixed error has nothing to do with the measured distance. That is, no matter how far the measured actual distance is, the total station will have a fixed error not greater than this value.
1ppm×Dkm represents the proportional error, where 1 is the proportional error coefficient, which is mainly caused by the instrument frequency error and the atmospheric refractive index error. ppm means parts per million (a few), and D is the distance value actually measured by the total station or rangefinder, in kilometers. As the actual measurement distance changes, the proportional error part of the instrument also changes proportionally. For example, when the distance is 1 km, the scale error is 1 mm.

For a total station or rangefinder with a ranging accuracy of 1mm plus 1ppm, when the measured distance is 1km, the ranging accuracy of the instrument is 1mm plus 1ppm×1(km)=2mm, that is to say, the total The distance of the station instrument is 1 km, and the maximum ranging error is not more than 2mm.
3 seconds is the time for ranging

1. Measuring range

2. Measurement accuracy

3. Where to use

And when the accuracy requirement is not high. Suggestion - "ultrasonic range finder" can be selected.

Suggestion - You can choose "handheld laser rangefinder as shown in the left picture".

Suggestion - buy "telescopic laser rangefinder" (ie: laser rangefinder telescope).