This model is designed for small area flow rate calibrations. The top layer will have solid infill in length starting from slightly less than 0.2mm to slightly less than 10mm. 

I picked those lengths because those are the ones worked the best for my past experience. However, there are also smooth transitions between each length. If you wish to set more points in the small area flow calibration. A simple linear interpolation will let you find the length of the extrusion on the top layer between two lengths.

Please follow the print instructions closely. Missing any steps will result in generating wrong gcode and cause the entire calibration not working properly.

Instructions to print:

1. Before doing small area flow compensation, you should already dialed in your extrusion multiplier and also your pressure advance settings. Whenever you change these settings, likely you will need to rerun a small area flow compensation. 
2. Find the specific model that matches with your nozzle size, layer height and line width. If you couldn't find one below, leave a comment and I can generate one and upload it.
3. Import the model into your slicer with small area flow compensation feature.
4. Set Wall Loops to 3.
5. Set Solid Infill Direction to 90 degrees.
6. Make sure your outer wall line width, inner wall line width and solid infill line width matches with the file. This is critical.
7. If your top layer solid infill line direction doesn't look like the picture below, rotate your model for 90 degrees so the top layer solid infill lines are parallel to the short side of this model.

Once printed, you will be able to examine the top surface quality of different length extrusions on the top layer. Increase and decrease flow rate of the small area compensation. Checkout teachingtech's video explaining values in the small area flow compensation box: 

I use google sheet to keep track of my trials and smooth the flow compensation so I don't get a choppy line: