GIS » Gisaf

Tom has reported that the well head (distance between the top of the casing and the ground level) of Dana well has changed, being +0.86 meters from the ground, starting from the 26th of July 2021.
Before the correction factor needed to calculate the well water level as referenced to the mean sea level was +0.18 m (meaning 18 cm above ground level).
From the 26th of July 2021, according to Tom, the correction factor has become +0.86 meters.

The problem now is that for Dana we have all readings (referenced to the sea level) before the 26 July 2021 calculated using 0.18 m, and from the 26 July 2021 a value of 0.86 m should be used instead.

How to do this in Gisaf so that it can be displayed automatically without compromising previous readings?

Before the 26th of July 2021, readings were computed by Gisaf as follows:
Reading referenced on mean sea level = altitude (48 m) + correction factor (0.18 m) - well reading
Example: on the 29th march 2021, the reading was 24.54, so the reding on sea level was 48 + 0.18 - 24.54 = 23.64 m

After the 26th of July 2021, the computation should instead be as follows:
Reading referenced on mean sea level = altitude (48 m) + correction factor (0.86 m) - well reading

So, for the 26 July 2021: Tom's reading was 26.74, the value referenced to sea level shall be: 48 + 0.86 - 26.74

Bala will go on entering the values into Gisaf, deducting the new correction factor instead of the old one. But the computation with respect to the sea level should be done now differently.

How to do it?

Giulio