By print a calibration block and get the z-height and extrusion multiplier, the reference is about basic calibration.
Design a 20mm cube for printing and print it out. When you are done, check to see if you have a 20mm cube.
You may need to adjust your z-height, which in this case is referring to bed to nozzle distance on layer one. You are looking for a proper fill, adhesion, and print width. Ex. 100% fill should have lines just touching each other without gaps or more than a very slight overlap. Print width of a single line should somewhat match your S3d settings , maybe .40ishmm wide. Z-height can also affect your overall height and bottom layer perimeters.
Your extrusion multiplier can help find the proper line print width and also correct some issues, such as bulging corners or helping to compensate for a slight clog when you just want get a print done and clean it out later.
3D printing is a dance of many settings playing off each other. The important thing to remember is that filament printing is not the same as metal machining. You will get some fluctuations in tolerances, etc. so don't spend hours chasing down .005 precision. You should expect a reasonable tolerance of around .10ishmm at best on your cube across the flats.
Most of your time diagnosing issues will be spent getting the first layer dialed in. It really sets the scene for the rest of the print. A bad first layer practically guarantees a print fail. A good first layer means you can walk away and go do other work. Sure, you will have other issues occur, but layer one is where problems are most evident and can be nipped in the bud.
Once you have experience you will be able to just watch the skirt of a print run and be able to diagnose many issues visually. Don't worry the tweaking and tuning gets more natural and easier to get your head around as you progress. Once you get the machine performing well in general, you will only have to take a few extra seconds to fiddle with things to optimize them for a specific print or filament.
