The ECG and HRV calculation
The ECG - i.e. the derivation of the electronic impulse of a heartbeat - serves us as the basis for calculating the heart rate variability! We tried out all the common belt systems for a long time in advance and then came to the decision to build an ECG derivation after all. The data accuracy factor more or less "forced" us to do so. The most accurate possible determination of the R-waves and their temporal distance is a basic requirement to be able to calculate the HRV sufficiently accurately.
The advantage of an ECG is the precise recording of the R-wave - the most definite point in time in the course of a heartbeat. The difference to all non ECG measuring systems lies on the one hand in the accuracy (measuring accuracy of the vital monitor 1msec by interpolation) and on the other hand in the verifiability of the ECG. This makes it possible to avoid or eliminate incorrect measurements resulting from a faulty ECG or ECG altered by extrasystoles.
If breaks and inconsistencies, such as outliers, are found in the course of a measurement, these are automatically cleaned up in small amounts (up to 15%). In addition, quality assurance can be performed on the basis of the ECG. Non ECG-based measurements do not provide the possibility of cleaning and thus error correction.
For the extrasystoles, we can also offer an automated cleanup (up to 15%). If there are too many, the affected measurements must be deleted. Extrasystoles are heartbeats that are not normal, but occur too early and thus have a strikingly short time interval to the heartbeat before, but a very long time interval to the heartbeat after. The standard deviation of the measurement series (=heart rate variability) can be massively distorted by this.
It is therefore advantageous to achieve the highest possible measurement accuracy with an ECG and also to be able to use this information for error correction. You would not entrust a carpenter with your new made-to-measure kitchen if he had a measuring tape that has a mark only every 2 cm and is also made of stretchable rubber!