Monthly Sales Pareto Analysis

I have a spreadsheet of sales transactions and I want to understand, at a glance, how many units each product moves from one month to the next and which items consistently make up the bulk of my volume. In practical terms, that means two things:

1) a month-over-month comparison of units sold, and
2) a Pareto chart that highlights the 20 % of SKUs driving roughly 80 % of sales each month.

You’re free to work in Excel, Google Sheets, Power BI, Tableau or another mainstream tool—whatever lets me filter by month, drill into a product line and instantly see shifts in contribution. I’ll supply the raw CSV; you return the cleaned file, a dynamic report/dashboard, and a brief note (two-three paragraphs is fine) calling out any notable spikes, drop-offs, or outliers you spot.

Accuracy and clarity matter more to me than flashy visuals, so please keep formulas transparent and label every axis, slicer and column. If something in the data looks questionable, flag it rather than forcing it to fit the model.