Comment 37 for bug 803791

running Windows 7, and Inkscape 0.48.4, I have not been able to reproduce the problems mentioned in comment 27.
- part of the problem may be related to the use of mm rather than pixels. In Inkscape, the native unit is the pixel, so any use of mm requires two separate conversions. One conversion will be done in C code in the gui, to convert from mm to px. Then the second conversion will be done in Python, in the Measure extension, to convert from px back to mm.
- part of the problem may also be related to the fact that the gui will sometimes report a visual bounding box size, which includes the stroke width, where you need to see the geometric bounds in this case. The geometric bounds can be obtained from the XML editor.

In any event, attached is a demo obtained in Inkscape 0.48.4. In all cases, the dimensions were confirmed in the XML editor, just to make sure they were correct.
- circle radius = 100 px. Expected circumference = 628.31853, actual calculation = 628.3263, error = 0.001 %, which is noticeably less than the error reported in comment 27, which was about 0.013 %.
- rectangle width = 100, height = 25 px. Circumference = 250 px.
- line horizontal distance = 200, vertical = 150 px, length = 250 px.
- in both cases the calculated length from the measure extension agrees with the expected