How can you calibrate extrusion multiplier value in Slic3r WITHOUT changing printer settings in memory? Most tutorials ask you to change the printer settings using the The command M92 E420 will set the new value which can be saved to memory (so that it is available after a printer power off/on cycle) using M500.

But I just want to modify the Extrusion Multiplier in Slic3r's settings. It's default at for each filament, and I'd like to modify this by adding a profile for each roll I have after calibration.



What's the best way to do this? If I measure extruding 100mm and checking how much is left, what is the formula used to get the new EM value?
Divide the amount overextruded by the desired amount. If you wanted 100mm but got 101mm, that's 1mm extra, or 1% over. Use an extrusion multiplier of 0.99 (1% under) to compensate - AND THEN DO ANOTHER TEST to confirm.

This modifier will be used by Slic3r to generate E values in your gcode without flashing anything. 

I recommend saving this recipe with an intuitive name, like Acme Green PLA.