Rescaling involves the board dimensions (I typically use inches because the ratio wants to be in inches) to the size of the viewbox in the svg file. It isn’t visible ourside of the svg, but it is important to Fritzing if we want to use automated tools to check parts (which I do). The ratio comes from the part file format at
at the bottom of the About Svgs section (itself near the bottom of the document)
“Now about measurements and SVGs. One of the pleasures of SVG is that the format can support extremely accurate placement and sizing. At the top level of the SVG, there are three attributes, width, height, and viewBox. …”
What I do in Inkscape to correct the scale when it is incorrect is here (it is a pain in the ass I will admit!):
In pcb after doing this you need to verify that the pads have not changed to ellipse during the rescale (as an ellipse won’t generate a hole in the gerber). I generally run the result through FrtizingCheckPart.py (available here):
which checks for this and various other errors.
Peter