Linear extrapolation tag
A linear extrapolation tag is a very simple estimate of what the future value of a tag will be by taking the current value of the tag and adding the increase over the last x time. For example, if a tag currently has a value of 10, and the value 5 minutes ago was 8, then we would extrapolate that the value in 5 minutes will be 10 + (10-8) = 12. An obvious requirement is that the tag behaves somewhat linearly within the scope of our use case. Below are some examples where we could use such a tag.
Predict that a tank will be empty in the next hour
Predict whether performance will drop below a threshold the coming week
![[en] Linear extrapolation example](image/uuid-fe61c529-72ed-eec1-587e-332c54000dea.png)
We estimate what the level will be 4 minutes. Since we know the level cannot be negative, we use the max function to have 0 as the lower limit.
Anmerkung
Linear extrapolation will always be a simplification of your process. If you think a more custom formula can predict future values better, don't hesitate to try that.
Warnung
To actually visually compare the prediction to the original tag, and project a value into the future, you want to shift your formula tag forwards in time (by the same shfit you have in your formula). For monitoring purposes, however, make sure the tag is NOT shifted forwards. Values beyond the current time will not be checked by the monitoring service, so shifting the tag into the future for the monitor will actually delay your monitor alerts, making them useless (as you might as well have monitored on the original tag then).