Two queries; (1) Waterfall with negatives | (2) Line chart with negatives

Also, probably should have added that in the upload:
'Opening' actually refers to the closing cash reserves of each month (don't know why I called it opening)
'MP' means midpoint between the current month and the next month (CM + NM / 2), but this is only calculated when both CM & NM are both positive or both negative. When one is positive and the other is negative, then the MP value is zero
'Positive' under a month column gives a value where the closing cash reserve for that month is positive. 'Positive' under an 'MP' column gives a value figure if the midpoint between CM & NM is positive
'Negative' under a month column gives a value where the closing cash reserve for that month is negative. 'Negative' under an 'MP' column gives a value figure if the midpoint between CM & NM is negative

I have to have two data series; one for values above zero ('positive' - coloured green) and another for values below zero ('negative' - coloured red) as I'm not capable of the type of formatting you suggested in your first post, so this is an easy workaround for me. But having two data series necessitates the use of a 'midpoint' function, so to give the appearance of a singular line chart.