Question

Someone lent me a book and they told me they left something inside and the picture attached shows the note that they left for me and I know what the text means but I have no clue what the equation means so can anyone help?

Answer 1

'∂' -- means a partial differential

'Δ' -- means a change in some variable.

'σ' --means 'sum' and 'deviation'.

The text says something about the world turning so maybe the equation has something to do with that? Maybe it is the equation for the earth's rotation. Sorry I can't find anything else, but I hope this helps a bit!