The idealized diode threshold is a checked energy boundary. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Source voltage supplies energy per charge
Charge 2 coulombs through source voltage 3 volts supplies 6 joules.
Esource=2⋅3=6J
Equality conducts in the toy threshold
The supplied energy and barrier are both 6 joules, so accepted is 1.