First, my apology for such late reply. Some how many of my blog comment notification emails got automatically routed to the clutter folder in outlook. I was just re-discovering how many conversation I missed.
To address your problem of predicting sales, I think you can start by setting up a simple linear regression model between the various predictor/operational metric over time (e.g. holidays, weekday vs weekends, supply chain data, etc.) and your sales data over time (e.g. daily sales, or weekly sales). Then once you solve that regression equation, the resulting coefficient would be able to give you the month predicted sales once you plug in the predictor/operational metrics, you will get a prediction of sales.
This does require you to have some statistical skills of setting up regression models and use packages and tools to solve it.
I hope this helps. Let me know if you need to dig deeper.
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