Flow Calibration Box

It's a box to test the flow rate (or extrusion multiplier) of your slicer to fix over or under extruding. It is also designed to fit a regular 20x20mm calibration cube into two of these.

To test your flow rate, simply print one of these.
Then, measure the width of the walls and they are supposed to be 0.8mm wide but if they're not that's ok because that's what we're trying to fix. So measure the walls and find the average width of them, now we'll do some simple math.
Desired width (0.8mm), ÷ your average width (which is what we got in the previous step), × YOUR CURRENT FLOW RATE, = your new flow rate
Now just print one of these WITH YOUR NEW FLOW RATE and measure the walls and it should be good.

Update:
I noticed that when I sliced it there were extra outer wall lines on two sides meaning that there was a little gap there (Thanks Tinkercad) and the bottom was 1mm thick. So I fixed the gap and made the whole thing 0.2mm shorter from the bottom meaning when you encase a calibra