Your canvas settings can be accessed from the top-right Settings button.

Show Ruler

Show/hide ruler on the drawing canvas. The canvas ruler is useful if you need accurate measurements on the line/shapes created on the drawing.

Snap to grid

This option allows you to use snap to grid for precision placement of drawing shapes and lines. If you uncheck this option, then placement of shapes and lines will only be approximate.

Grid Snap

This option applies when Snap to grid is turned on.

This option will set the visible grid-line size relative to the ruler unit of measurement.

It allows you to set the precision of the shapes when moving them around.

It uses a grid specified by pixels on the screen.

For example, if I set the snap to every 100 pixels, the grid lines will be quite spaced out.

However if I set the snap to every 20 pixels, then the grids are much smaller and allow for more precise snaps.

Unit of measurement

This options allows you to set a measurement type for this drawing (eg: metres, kilometres, centimetres, millimetres, pixels or none).

This allows you to set the measurement to suit the type of drawings you are preparing.

For example, if you are doing site plans for a house inspection you would likely use metres as the unit of measurement.

This unit will also be displayed on the ruler

Ruler pixels per unit

This option will specify how the ruler should be spaced based on the selected unit of measurement.

For example, if the pixels-per-unit is set to 100 pixels, then every 100 pixels will specify the next unit on the ruler.

However, if I set the pixels-per-unit to 50 pixels, you'll notice that the ruler is spaced much closer together

Example:

This example shows a pest inspection on a house with a ruler showing metres and a snap to grid precision of 1 metre.