Title block
The bordered panel, usually along the right edge or the bottom corner of a sheet, that says what the drawing is: project, sheet name and number, drawn-by, date, revision letter, and the scale the sheet is drawn at.
A drawing without a title block is an anonymous picture. The panel is what turns a sheet into a document of record, and it is the first thing a contractor looks at, because it answers the two questions that matter before any line on the page can be trusted: which version is this, and how big is what I am looking at.
Why the scale lives there
Scale is a property of the whole sheet, not of any object on it. Writing 1:100 next to a corridor would say nothing about the room beside it, so the statement belongs somewhere that governs the page. The title block is that place, and by convention it is also where a scale bar sits, so the drawing stays measurable after it has been photocopied at ninety percent.
That is the failure mode worth knowing about. Scale as a ratio is only true at the original sheet size. A drawing printed to a different paper size, or exported at a different page setup, keeps the number and loses the truth of it. A drawn scale bar survives, because it shrinks with everything around it.
Reading it in a leasing context
The revision letter is the other line to check. Marketing a floor from an old revision is how a partition that was moved eighteen months ago ends up on a listing. The panel states the revision plainly, and it is quicker to check than to reconstruct.
How StudiO uses it
On a vector PDF, StudiO takes the scale from the title block and applies it to every wall segment it measures. On a raster sheet, a photograph or a scan, there may be no readable panel at all, so the scale is estimated instead. StudiO states which it did, so you know what the number is.