I can manually set up height and width of the picture (in pixels). It is possible only for 3 decimal places. I´m afraid. It´s too little.
I would like set up the number of decimal places after the decimal point (about 8 - 10 decimal places).

For example:
Now:
height = 123.456 (px)
width = 122.447 (px)

I need:
height = 123.45612345678 (px)
width = 122.44714578966 (px)

Thank you. Paul

You could try resizing the page to a rectangle with height and width values set via the xml editor (Shift+Ctrl+X).
Though even that way the rounding error won't keep more than 5 digits intact, so you may draw in a bigger scale.