BASIC manipulates graphics with respect to the problem coordinates，which do not depend on hardware pixels.

**SET WINDOW**

A SET WINDOW statement introduce a problem coordinates on the drawing pane.

`SET WINDOW `

*left* , *right* , *bottom* , *top*

introduces the coordinate system on which the *x*-coordinate of the left-hand edge is *left*, the *x*-coordinate of right-hand edge is *right*, the *y*-coordinate of the bottom-end is *bottom*, and the *y*-coordinate of top-end is *top*, where *left* , *right* , *bottom* and *top* are numerical expressions.

` SET WINDOW -4,4,0,8`

The range of x-coordinates shall be from -4 to 4，the y-coordinates from 0 to 8.

The initial aspect of the drawing pane is square.

Thus, the ratio of the vertical length to the horizontal length is 1:1 when the coordinates are set so that *right* `-`

*left* =*top* `-`

*bottom*.

If no SET WINDOW statement has been executed, the left-hand edge coordinate and the bottom-end coordinate are 0, and the right-hand edge coordinate and the top-end coordinate are 1.

**ASK WINDOW**

`ASK WINDOW x1, x2, y1, y2`

assign s the current coordinates to numerical variables x1, x2, y1, y2.