Tom draws the horizontal line and marks out the length dimension

Tom uses his compasses to mark out the crossover points for the vertical line from the 'length' marks. This method ensures a true right angled cross over of the horizontal and vertical lines.

Top crossover points drawn, now to do the bottom ones

Once the crossover points are drawn, Tom will draw
the vertical line

 

Drawing in the vertical line

The horizontal and vertical lines are now drawn

Tom checks that the the horizontal 'end' marks are accurately placed

Tom now sets the compasses from the centre crossover point to a horizontal 'end mark' in preparation for marking out the points for the "pin insertions" on the horizontal line. That measurement is the one required for accurately marking out those pin insertion points on the horizontal line.
The method for marking out now follows:

Tom now marks out the insertion points for the pins from the lower point

Tom marks out the X from the top vertical point

Pins are now pushed through the 'X's' from the reverse side

Gauging the size of the loop required for drawing the oval.
It should go from either X to the opposite end mark

Tom uses a piece of veneer cut to size to tie the loop around
to ensure accuracy of loop size when removed from the 'template'

Tom places his pencil point in the loop ready to draw the oval

Keeping the loop under "just sufficient"  tension - Tom draws the oval

Over half way now. Note that the loop forms a triangle while drawing

The oval is nearly finished

The oval is completed

The finished result.