MODULE Unit;

(* Defines constants and 
   procedures for various units 
   of length. The lengths are
   defined in terms of the units
   of Juno's coordinate system,
   which are PostScript points
   (equal to 1/72 of an inch). *)

CONST 
  In = 72.0, 
  Ft = In * 12.0, 
  Cm = In / 2.54, 
  Mm = Cm / 10.0;

(* "In", "Ft", "Cm", and "Mm" 
   are the size (in points) of 
   one inch, one foot, one 
   centimeter, and one 
   millimeter, respectively. *)

(* Juno's coordinate system 
   uses screen-independent 
   units, but there are cases 
   in which screen-dependent 
   units could be useful. This 
   is most often the case when 
   PostScript output is not 
   being generated, and it is 
   important that the 
   quantization error induced 
   by the discrete pixels on 
   the screen not effect the 
   regularity of the drawing. 
   For example, it would be 
   more convenient to use 
   screen-dependent units to 
   draw a series of 
   evenly-spaced horizontal 
   lines. The following 
   procedure can be used to 
   obtain the screen-dependent 
   size of a single pixel. *)

PROC x, y := Pixel() IS 
  SKIP 
END;

(* "x" and "y" are the 
   horizontal and vertical size 
   (in points) of a pixel on 
   the screen on which Juno is 
   running. Use this procedure 
   in your Juno programs with 
   care, since it will cause 
   your program to be 
   screen-dependent. *)