"10 transparent sheets with points. 10 drawings having six differentiated curved lines. A graph (having 100 units horizontally, 20 verticaly) and a straight line, the two last on transparent material.

Place a sheet with points over a drawing with curves (in any position). Over these place the graph. Use the straight line to connect a point within the graph with one outside.

Measurements horizontally on the top and bottom lines of the graph with respect to the straight line give a 'time bracket' (time within which the event may take place) (graph units = any time units)."