The detailed question was:
The monthly Coppock [of the S&P/ASX All Ordinaries price index) has been trending down for the last 7 months and is currently well below zero. Is there some way that one could calculate / estimate (into the future) at what level of the XAO it will turn up e.g. if the XAO is above 5300?
The Coppock trending down is not a part of its interpretation. The only signal is when it has fallen below zero and turns up. So, we have a set-up on the price index Coppock and now the Total Return Coppock.
When those signals appear is driven by the monthly close of the relevant index. There is no way I know of to predict the signal well in advance, which would involve predicting the relevant index monthly closes. It is probably possible only in the last days of a month when the Coppock is negative. Insight Trader calculates the Coppock assuming the last daily reading is the end of month reading, so if you judge that the market will close around the latest value of the relevant index, you could make a prediction that a signal will occur at the end of the month. Frankly, in the time frame of an investor, I doubt that is of much value. That said, be careful with Insight Trader, because it does not round the value to the nearest 10 as Coppock did to eliminate “noise” signals close to the zero line (which are not good signals anyway).
Bear in mind that the Coppock is only one tool and it should not be given importance beyond its single goal of signalling when to consider buying uptrending stocks for long term capital appreciation. It is an investment tool, not a trading tool. There are far better tools for traders, such as MACD, RSI etc.
If you want to calculate the closing index value for the current month that would generate a signal, that is possible using my spreadsheet – you could put in numbers by trial and error for the current month, or build a new column that would give you a value 10 higher than the value at the end of the last month.