Visual Flow Calibration Test

This model tries to help you visualize if your flow is set correctly. If you see gaps between perimeters/walls or gaps between parameters/walls and solid infill, you are probably underextruding and the flow needs to increased. If there is amassed material and even though you print it slow it's not as clean you might be overextruding.

Be sure to use sufficient infill or you might get gaps because of a low amount of infill instead of low flow (see print settings below).
Be sure your slicer uses minimum layer time and/or print slowly or the speed could affect the visualization by overheating the extruded filament and the print could look like it was overextruding.

I'd start with printing one model with an extrusion multiplier of 0,95 aka flow of 95%, one with 1 (100%) and one with 1,05 (105%) to see the differences. Then fine tune.

Hope it helps.