Hello! I would like to create a new equation using a specific variable.

This variable shows the total energy every specific time (refresh every 5 sec). I aim to create an equation where will be done a subtraction between this variable at 00:00 of this day (subtracter) and the instant Value of energy (subtrahend) as i take it from Mango.

Let's assume E is the total energy variable, i would like to create an equation like: E(t)-E(00:00-start of the day). Is any way to implement this?

Thanks in advance,

Nikos.