## Internal Zooming

GREG has the possibility of zooming a plot being created. Use command ZOOM to do it. ZOOM X1 X2 Y1 Y2 will compute scale factors to match the designed area (in Physical Coordinates) to the screen, preserving the aspect ratio. ZOOM OFF restores the full screen, ZOOM REFRESH redraws the plot with the current zooming factor. Without arguments ZOOM calls the cursor, and several keys can be used to control the zooming factor :

- “0” turns off zooming and displays the full plot page. The previous zooming factor is not destroyed, so that typing a space (see below) will restore a Viewing Window of same size as the last one centered on the cursor position. The cursor position is not modified by the command itself.
- “ ” (space) executes the standing zooming operations. With “0”, it is the only effective command. The zoomed area is centered around the cursor position and can be delimited using command B.
- “Z” increases the zooming factor by 1.414 and draws the corresponding box around the zoomed area. The zooming is deferred until “ ” has been struck, allowing zooming factors to be changed by any power of square root of 2. The box drawn around the zoomed area is not a part of the current plot, and will not be visible in a Hardcopy for example.
- “-” decreases the zooming factor by 1.414, and draws the corresponding box if visible.
- “B” draws a box delimiting the area to be zoomed.
- “A” to erase the alphanumeric screen
- “E” to exit...

Any other gives you the cursor position. Zooming can be used for example to enlarge part of a complex drawing to make precise annotations. Note that the zooming has no effect on the hardcopy.

On X-Window systems, the zoomed area normally appears in another window. The mouse can be used instead of the keyboard for some actions:

- left button: as spacebar, execute the zoom
- middle button: increase zooming factor by 1.414
- right button: exit