Assumptions - Circuit Builder
The applet lets you build an electric circuit containing batteries, resistors, light bulbs, switches, ammeters, voltmeters, and calculates currents, potentials, and powers dissipated in the circuit.

The applet takes the resistance of any wire segment between two adjoining grid points to be unequal to zero. The fixed value for this resistance is 1×10-9 W. This value is negligibly small in most, but not all situations. Textbooks usually take the resistance of wires to be zero, to simplify the calculations. For most circuits constructed with the applet, you may take the resistance of the wires in the circuit to be zero in your calculations without making a noticeable error.

The applet takes the resistance of a closed switch to be equal to 1×10-9 W also.