The RectGC ("Rectangular Grid Coordinates") command (like its opposite, the PolarGC) command, affects how the coordinates of a point on the graph screen are displayed. When RectGC is enabled, the coordinates of a point are displayed as (X,Y).
The X and Y coordinates of a point are interpreted as the horizontal and vertical distance from the origin (the point (0,0)) Up and right are positive directions, while down and left are negative. For example, the point (1,-2) — that is, the point with x-coordinate 1 and y-coordinate -2 — is one horizontal unit right and two horizontal units down from (0,0).
Of course, coordinates are only displayed with the CoordOn setting; however, with CoordOff, RectGC and PolarGC are still useful, because in a variety of cases, the coordinates of a point are also stored to variables. With RectGC enabled, they are stored to X and Y.
The following situations involve storing coordinates of a point to variables:
- Graphing an equation
- Tracing an equation or plot
- Moving the cursor on the graph screen
- Using the interactive mode of one of the 2nd DRAW commands
- Using one of DrawF, DrawInv, or Tangent(
- Anything in the 2nd CALC menu.