I hope I have understood your question correctly.
You can resize an image in the "position and size"
panel on the right hand side menu, select the crossed arrow icons, and fill in the size you want.
If working in inches gives you too much or too little sizing try changing your unit of measure to mm or cm by opening the view menu in the top bar and selecting ruler units
Here is a little cheat sheet showing the effects of clicking on the size changes in increments. I hope this helps. I use ecal2 and you don't say which scal you use but I think they all do it the same.
Screenshot 2015-03-17 08.03.02.png [ 39.06 KiB | Viewed 768 times ]
eCAL 2- How to Resize.scut4.png [ 191.63 KiB | Viewed 768 times ]
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Mac 10.9.5 Yosemite, eCAL 1.506, ECAL2.023, SCAL4Pro, Export Plug-in, Inkscape 48, iPad/scal3