This Graph menu command creates a new coordinate system and marks it as the active coordinate system. The type and scale of the created coordinate system depends on your selections, as described in this table.

(If you choose a command, such as Measure | Coordinates, that requires a coordinate system but you haven’t created one in your sketch, Sketchpad defines and marks a coordinate system for you.)

Selections |
Command |
Result |

One point |
Define Origin |
Square coordinate system centered on the selected point with default unit scale |

One circle |
Define Unit Circle |
Square coordinate system centered on the selected circle with unit scale determined by the circle’s radius |

One defining distance* |
Define Unit Distance |
Square coordinate system centered on a default origin with unit scaling determined by the defining distance |

One point and one defining distance* |
Define Unit Distance |
Square coordinate system centered on the selected point with unit scaling determined by the defining distance |

Two defining distances* |
Define Unit Distances |
Rectangular coordinate system centered on a default origin, with horizontal unit scaling determined by the first selected distance and vertical unit scaling determined by the second selected distance |

One point and two defining distances* |
Define Unit Distances |
Rectangular coordinate system centered on the selected point with horizontal unit scaling determined by the first selected distance and vertical unit scaling determined by the second selected distance |

Nothing or anything other than the above |
Define Coordinate System** |
Square coordinate system with default origin and unit scaling |

* A defining distance can be either a segment or a distance value.

** Define Coordinate System is disabled if there’s already a marked coordinate system.

As described in the table, some commands define a coordinate system with a default origin or default unit scaling. Sketchpad constructs a default origin as an independent point in the center of your window. The default unit scale is based on the current distance unit chosen in the Preferences dialog box, but can be adjusted by dragging the coordinate system’s unit point or axis tick labels.

Since most activities require only a single coordinate system, the Define Coordinate System choice (which defines an entirely default coordinate system) is disabled if your sketch already has a coordinate system. If you really want a second coordinate system, you must select the appropriate objects as listed in the first column of the table.

See also: