#### Standard deviation of the frequency deviations

Frequency is a key indicator for the operating security of the entire interconnected grid. In order to measure its quality, the frequency deviation is measured against the setpoint value every second and recorded. Then the statistical distribution of these values is evaluated over a period of 15 minutes by calculating the standard deviation of this distribution.

The frequency quality of a given month is derived from the statistical evaluation of the s values for that month. The s value below which the calculated values occur in 90% to 99% of the monitoring intervals is an indicator of the frequency quality of the grid.

#### Number of corrections to the synchronisation per month

The number of corrections and the number of total correction hours per month are monitored.

#### Total frequency deviations greater than 50 mHz

The proportional amount of time during which the deviation of the grid frequency is greater than ± 50 mHz relative to 50 Hz is also a useful indicator.

All indicators mentioned above are calculated in Laufenburg by Swissgrid and displayed on a graph.