Appearance

• A line is drawn from each cell to the equation rendered from it, with an arrowhead at the equation end.
• A run of cells drawn as one indexed equation (see Tables) cannot be answered with a line, because a line reaches one cell of the run and says nothing about the rest. Those are marked down their right-hand edge with a semi-transparent strip of colour, and the equation they belong to is bordered in the same colour. The pairing is what links them.
• Each run takes its own colour, so several tables can be traced at once and told apart.
• Nothing is written to your cells. The strip, the lines and the border are shapes lying over the sheet, and they all come off together. A cell's own fill, borders and font are never touched.

Usage

• Rendering new equations shows the marks for a couple of seconds by itself, so you can see where each one came from without asking. They then take themselves away.
• Trace is a switch, and sits beside Equate and Unit because it is the same kind of control: it says how the next render behaves rather than doing something to the sheet. Switched on, the marks a render shows are kept instead of leaving.
• The switch never touches marks already on the sheet, in either direction.
• To show or hide the marks for particular cells, select them and hold ⌘ on a Mac or Alt on Windows while clicking Trace. Pressing it again over the same cells takes them down.
• Marks belong to the equation they were drawn from. Rendering somewhere else on the sheet leaves them where they are; they come down when the equation they belong to is asked about — by tracing those cells again, or by rendering or erasing them.
• A grouped run is reached through any of its cells, not just the first, so selecting the middle of a table and tracing marks the whole run.