I have two spreadsheets; one an earlier version and one that reflects the current state after many alterations and updates and I wanted to document all the changes.
So I tried to put them side by side so I could manually compare them row-by-row.
There are two buttons on the task bar (one for each window) but clicking them loads each spreadsheet in exactly the same window. They effectively overlay each other.
After doing some research, I found you need to click Window / Arrange / Vertical and hey presto it's done.