A decade resistance box contains a series of resistors usually with values 1, 2, ... 9 ohm, and multiples (or fractions) of 10, covering two or more of such decades.
With manual switches one resistor out of each decade can be selected and connected in series. In this way, an arbitrary resistance value can be created between the lowest available resistance and the series of all the highest values in each
decade. A decade resistance bank can, therefore, be considered as a step-wise variable resistor, with steps equal to the lowest available resistance.
The resistance bank shown here has a range from 0.05 ohm to 0.1 Mohm, so over 6 decades.