Slicers build walls from whole lines, not a continuous dial
It is easy to think of "wall thickness" as a continuous setting, but a slicer actually builds a wall from a whole number of extruded lines at your configured line width. A target thickness that does not land on a clean multiple of that line width creates ambiguity that different slicers resolve differently, some thin out the extrusion to force a fit, others round to the nearest whole line. This planner surfaces that ambiguity directly instead of letting it happen silently.
How the planner works
Your target thickness is divided by the line width (from your nozzle, or a value you enter directly) to get an exact line count. If that count lands close to a whole number, the target maps cleanly. If it falls meaningfully between two whole numbers, the tool flags a partial-line ambiguity and shows both the rounded-down and rounded-up options with their resulting thickness, so you can choose deliberately rather than let the slicer decide for you.
Worked example
A 1.6 mm target wall at a 0.4 mm nozzle (about 0.45 mm line width): 1.6 divided by 0.45 is about 3.56 lines, a partial-line ambiguity. The tool shows 3 lines (1.35 mm) versus 4 lines (1.80 mm) as the two clean options and recommends rounding up for a stronger, more predictable wall unless material savings matter more for this specific part.
A common mistake
A frequent error is leaving a partial-line ambiguity to the slicer's default behavior without ever checking what that default actually does. Some slicers silently thin the extrusion to force a fit, quietly weakening the wall in a way that never shows up until the part is under load. Always check your specific slicer's actual behavior on an ambiguous target rather than assuming it rounds the way you would prefer.
Limitations
This maps your target thickness to whole wall lines using your nozzle and line-width assumptions; it does not simulate your specific slicer's partial-line handling, which varies between slicers and versions. Confirm the actual sliced wall count in your layer preview.