Thickness matters far more than most people expect
Beam deflection under a cantilever load scales with the cube of both length and thickness, which means small changes to either dimension have an outsized effect compared to a linear change. Doubling an arm's thickness does not halve its deflection, it cuts deflection to roughly an eighth, all else equal. This planner uses that relationship to compare design changes against each other for ranking purposes, without pretending to output a real millimeter deflection figure your printer will actually match.
How the comparison works
A relative deflection index is computed from length cubed divided by a stiffness category times thickness cubed, standard cantilever beam-theory proportionality. The result shows how much doubling thickness alone would improve that index, since thickness is consistently the highest-leverage single dimension to change. A shorter span is offered as the comparably effective alternative when adding bulk is not acceptable.
Worked example
A 40 mm long, 3 mm thick arm at moderate (PETG-like) stiffness: the relative deflection index highlights how much stiffer the same arm becomes at 6 mm thickness, roughly an eighth of the current deflection, framed explicitly as a ranking tool for comparing this change against alternatives, not a predicted number of millimeters.
A common mistake
A frequent error is thickening a cantilever uniformly along its whole length when the real deflection happens mostly near the fixed end. A tapered cross-section, thicker where it attaches and thinner toward the tip, often achieves similar stiffness with less added mass than uniformly thickening the entire arm, but this planner's simple comparison assumes a constant cross-section unless you model the taper as a separate, shorter effective length.
Limitations
This is a relative comparison for ranking design changes against each other, not an absolute deflection in millimeters or a real modulus value in MPa. It assumes a simple end-loaded cantilever; a different load pattern or a tapered cross-section changes the real relationship. Validate an actual functional deflection with a real test part.