Interface

The main window, its panels, and how to move around and select things in it.

Window layout

The main window is a dockable layout with a menu bar (File, Model, Options, Addons, Help, plus the traffic-light checklist at the far right) across the top, a thin control-panel ribbon just below it, and these panels arranged around a central canvas:

• Model Tree — the main left-side panel. It splits into a top Tools section, whose contents change with the active workflow tab (Geometry, Circuit, Mesh, Solver, Postprocessing, or Machine Parameters), and a bottom Model Properties section listing the regions, boundary conditions, coils, shapes and motion zones in the current model;
• the canvas in the centre — the geometry/circuit viewport where you draw, select and watch the mesh and the field;
• Log Bar along the bottom — every message Nabla and the solver print, including the line that explains a failed run (Options → Show Log Bar to toggle it);
• Coord Bar — the cursor's current coordinates, next to the log bar (Options → Show Coordinates);
• Field Legend Bar — the colour-scale legend for whatever field is currently plotted, shown once you are in the Postprocessing tab with a solved result.

The workflow tab bar sits at the top of the Model Tree, above the Tools section: Geometry Editor, Circuit Editor (hidden once the Thermal module is active, since a thermal model has no electrical circuit), Mesh, Solver, Postprocessing, and, for a model created through Addons → Machines, Machine Parameters. Switching tabs swaps the Tools section's contents and, on the canvas, which overlay (geometry, circuit schematic, mesh, or field plot) is drawn; it does not change what is selected or lose any work in another tab.

The Model Tree

Each entity list in the Model Properties section — regions, boundary conditions, coils, shapes, motion zones — behaves the same way:

• Click an item to select only it;
• Ctrl+click to add or remove an item from the current selection;
• F2 while an item is focused renames it in place;
• Delete removes every currently selected item;
• Double-click opens that item's properties dialog (Region Properties, Coil Properties, and so on).

Selecting an item in the tree and clicking it on the canvas are the same selection — the tree is simply a list view onto whatever Selection already covers.

Selection

Click a line, arc or circle on the canvas to select it; click empty space to clear the selection. Ctrl+click adds a shape to the current selection instead of replacing it, and clicking an already-selected shape again deselects just that one. Turn on Select Region Boundary Edges to drag a rectangle instead: every shape fully inside the rectangle is selected (a shape that only partly overlaps the box is left alone), and Esc cancels a rectangle you are still dragging.

Region and hole markers use the same click-to-add behaviour as drawing them: with the Add Regions/Add Holes tool armed, a plain click drops a new marker, while Ctrl+click selects an existing one instead.

Moving around the canvas

• Scroll wheel zooms in and out, centred on the point under the cursor;
• Middle-mouse drag pans;
• Double-click the middle mouse button resets the view to fit the whole model.

Zoom sensitivity is adjustable under Options → Application Preferences. Zoom is clamped to a fixed range so you cannot scroll the view into a degenerate scale by accident, and it always zooms toward the point under the cursor rather than the centre of the canvas, so you can zoom into a small slot detail without first panning to centre it.

A small axis indicator (labelled GCS, for Global Coordinate System) marks the drawing origin and the X/Y directions; hide it via the Show Global Coordinate System checkbox in Preferences if it clutters a dense model. The background grid itself has its own visibility checkbox next to the snap-mode radio buttons on the Geometry and Mesh tool panels — separate from grid snapping, so you can snap to the grid without drawing it, or draw it purely as a visual reference without snapping to it.

Application Preferences

Options → Application Preferences opens a tabbed Preferences window:

• General — show/hide the coordinate system, log bar and coordinates bar, tooltips and item icons, whether the welcome screen appears on startup, zoom sensitivity, and the Length Units (millimetres, centimetres, metres, inches or feet) and Time Units combo boxes;
• Geometry — grid spacing and grid line colour/width for the canvas's background grid (the same grid Grid snap locks the cursor to, see Geometry — snapping);
• Model Settings — the default element area used when meshing (see Meshing — mesh size) and the default axial length for a new model.

The traffic-light checklist

Three round lights at the right of the menu bar summarise whether the model is ready to solve: hover any of them for a tooltip, and hover the green one specifically to see the full checklist that passed.

• Red — a rule that would make solving fail is not satisfied: a shape with no boundary condition and no neighbouring region, a region with nothing assigned to it, an invalid time-step/frequency setting, or a motion-zone rule violation;
• Orange — every rule passes, but the model has unsaved changes;
• Green — every rule passes and the model is saved.

The checklist re-runs on essentially every edit, so it is always answering "if I solved right now, would this work" rather than something you need to trigger by hand. See Troubleshooting — the traffic light stays red for what to do about each case.

Keyboard shortcuts

Nabla is click-driven rather than shortcut-driven, but a handful of keys are worth knowing:

• Ctrl+S / Ctrl+Shift+S / Ctrl+O / Ctrl+N — save, save as, open, new model;
• Delete — removes whatever is currently selected in the active panel (shapes on the canvas while in select-edges mode, or the highlighted rows in a Model Tree list: regions, boundary conditions, coils, holes, motions, circuit elements);
• Esc — backs out of what you are doing one step at a time: cancels a drag-select rectangle, steps back through a multi-click tool (arc, offset) one placed point at a time, or clears the current region/hole selection;
• I — inverts the current shape selection (selects everything that was unselected and vice versa) while a select tool is active;
• F2 — rename the focused item in a Model Tree list;
• F1 — opens this manual (suppressed while a text field has keyboard focus, so it never fires by accident while you are typing a number).

While a drawing tool is placing a shape (line, arc, circle) or you are typing an offset distance, the numeric keypad enters a value directly instead of moving the mouse — see Geometry — precise numeric entry.

Next steps

• Geometry — drawing your first shapes.
• Regions & materials.
• Back to the contents.