Wherever you need a continuous manual change of something, you can use the knob.
In comparison to commonly used sliders, the knob has two fundamental advantages:

The position can be set very preciously, dragging the clicked mouse along any big radius.   It can be endlessly rotated round around.

The knob is utilised by the graph to adjust its scale (both or vertical only), but those features will be described in the next chapter.
The main use of the knob is the continuous adjustment of the function ext .
RESETTING THE KNOB - by double clicking the knob. The knob is set to its middle position and the value of ext is set to zero.
ext is the only function which depends on no variable. The user can force its value by the knob.
There are two main modes, defined by the switch "INCR" :

ABSOLUTE MODE (INCR deactivated) - the value of ext depends on the knob's deflection angle. If the knob is in the middle position (12 o'clock), the value is zero. Clockwise rotation rises the value along 0.5 (3 o'clock) to 1 (6 o'clock). Counter clockwise rotation lowers the value along -0.5 (9 o'clock) to -0.999 (6 o'clock). The step is always 0.001.   INCREMENTAL MODE (INCR activated) - the value of ext is incremental. The exact (zero) value is defined only by resetting the knob. By rotating the knob clockwise, the value of ext is incremented, rotating the knob counter clockwise, the value of ext is decremented. Increment or decrement step is always 1 and rotation is unlimited.

TIP: If the other range, step or incurvation of progress (for example logarithmical) is required, use ext as a part of more complex function.
Examples:
  a=9*ext-6   for a in linear interval -15 to 3
  a=(ln((ext+1)*1.175+1/eu)+1)/2   for a with the logarithmical incurvation and interval 0 to 1.