Prerequisites:

• scaling factors for converting data values to plot values have been determined.

Steps:

• determine the increment between steps

  x_increment:= increment((max-min)*60.0/(w_max-w_min));
  

  where max and min are the ends of the data range, and w_max and w_min are the corresponding points on the plot.
• determine the first label to be plotted:

  x:= round(x_min/x_increment+0.4)*x_increment;
  

• draw the tic mark, then increment the label position. Repeat until the position is off the other end of the plot.

function increment(x: real): real;
var e: real;


begin
    enter('increment');
    e:= int(log(x));
    x:= x / pwr10(Trunc(e));
    if (0 < x) and (x ≤ 0.1) then x:= 0.1
    else if (x ≤ 0.2) then x:= 0.2
    else if (x ≤ 0.5) then x:= 0.5
    else if (x ≤ 1.0) then x:= 1.0
    else if (x ≤ 2.0) then x:= 2.0
    else if (x ≤ 5.0) then x:= 5.0
    else then x := 10.0;
    increment:= x * pwr10(Trunc(e));
    leave('increment');
end;