The sum of row heights is wrong

[kobusb]

The sum of row heights is much more than the total height shown on the left ruler in "page Layout" view (Excel 2010) e.g. the space between top and bottom margins show as 25.9cm and 78 rows of 10 points each fit on the page giving a total height of 780 points or 27.52cm, an error of 0.62cm.
With larger row heights the error becomes smaller.
Does anyone know this happens?

 

[shg]

in general, Excel won't set rows to exact heights or columns to the exact widths you specify.

 

[kobusb]

I may be wrong but after some experimenting it seems that the row height is always 7.5% smaller. I tried different printer drivers and paper sizes.
Why would Excel make the row height 7.5% smaller than the setting?

 

[shg]

For me, it varies by printer, but Excel is a spreadsheet, not a CAD program.