Reading the preview

The G-code preview shows exactly what the nozzle will do — not a render of your model, but the actual toolpaths. Two minutes here saves a failed print.

Press P to switch between the model and the preview.

Colour by

The Colour by dropdown repaints the whole preview. Each mode answers a different question.

Mode	Answers
Role (default)	What is each line for — wall, infill, support, bridge?
Speed	Where does it slow down? Sudden slow patches often mean cooling limits.
Flow	How much plastic per second — the real load on your hotend.
Line Width	Where beads get thin or fat. Useful for checking thin walls.
Layer Height	Varies only if you're doing something clever with layers.
Acceleration	Where the machine is being pushed. Ringing usually starts here.
Fan Speed	Cooling, per layer.
Temperature	Per-layer nozzle temperature.
Layer Time	Which layers are so quick they won't have cooled.

In Role mode the legend doubles as a filter. Click a role to hide it — hiding infill to inspect the walls underneath is the most common move. Travel moves and seams are hidden by default; turn them on to hunt down stringing or a seam landing somewhere visible.

Roles are grouped so you can toggle a whole family at once: Shell, Fill & Surfaces, Support & Adhesion, Movement & Markers.

Moving through the print

• Layer slider — or ↑ / ↓ for one layer at a time.
• Show all layers vs current layer only — the stack, or one slice in isolation. Isolation is better for looking at a specific problem.
• Progress slider — scrub within a layer. → / ← step move by move, so you can follow the nozzle through a tricky bit.
• Hover any line for its role, layer, Z height, width, height and speed.

Folding it away

The legend and its controls are a tall panel sitting over the plate. Tap the G-code header at the top of the panel to fold it down to a single row — the layer counter stays visible, and the Slice button stays where it was.

Unfolded, the panel takes as much room as the screen has, so on a tablet or a desktop the whole legend and both sliders are visible at once. It only scrolls when the window is genuinely too short — and even then the Slice button stays put.

On a tablet or phone it starts folded, since the panel would otherwise cover most of what you're trying to look at. On a large screen it starts open. Either way, once you fold or unfold it yourself the slicer remembers, and stops guessing.

What to look for

Before your first print of a model:

• The first layer covers what it should and has your skirt or brim.
• Bridges actually span a gap rather than hanging in air — switch to Role and look for bridge-coloured lines.
• Supports touch what needs supporting and nothing that doesn't.
• The top surface is continuous, without stray dashes or gaps.

When something printed badly:

• Blobs or zits → look at seam placement.
• Stringing → turn on travel and look for long moves across open space.
• Poor overhangs → check fan speed and layer time on those layers.
• Ringing → check acceleration and speed around corners.

The stale-preview rule

The Re-Slice button turns amber the moment you change a setting or move a model. The preview you're looking at is from before that change. Re-slice before you trust it.