Hi threesixty,
Thanks Wayne and Yellow (can I call you Yellow? =: )
You can call me anything, but don't call me late for dinner 🙂.
A Numbers document with many Sheets (Tabs)

The Very Large Database (on the Stocktake Sheet) has (in reality) many more Rows and Columns.
The table on the Avocado Sheet pulls values from the Very Large Database using formulas. How can we help you with those formulas?

To view two Sheets at the same time,
Save your document (for example, threesixty)
Menu > File > option key > Save as... (for example threesixty temp)
Open both documents, drag to resize (hide the Format Panels to make this easier) and drag them side-by-side (I am using one monitor):

Just be sure which is the Master copy and which is the temp copy. Save the Master copy 👿 .
Regards,
Ian.