The Hummel array is actually a more practical variant of the Schlumberger array, easy to adapt to difficult working conditions. In practical terms is a half of the Schlumberger array, one of the power electrodes being placed at infinity perpendicular on direction of the array.
The computing of the apparent resistivity is done using the same formula as for the Schlumberger array, but to be accurate the resistivity is doubled.
Roa =2* V/I*PI* b^2/a
Using this method we can reduce the personal number necessary for the operation of moving the electrodes and also the measuring time. This technique is useful when the geological conditions allow its use – relative horizontal layers.