A method for determining relative positions of a plurality of slave units (200.1 to 200.n) connected to a stub bus with a master unit, wherein the stub bus comprises at least a power line and a ground line, wherein each slave unit (200.i; 200.1 to 200.n) is operable in different power modes, which are differentiated by effective resistances between the power line and the ground line, wherein each slave unit (200.i) comprises a voltage potential drop measurement unit arranged to measure a voltage potential drop across the power line and the ground line, the method comprising: the master unit, instructing each slave unit (200.i) to measure the reference voltage potential drop V i ref while each slave unit (200.i) is operating in a low-power mode; each slave unit (200.i), determining a reference voltage potential drop V i ref across the power line and the ground line while the slave units (200.i; 200.1 to 200.n) are operating in the low-power mode; the master unit, instructing each slave unit (200.i) to measure the positioning voltage potential drop ( V i pos) across the power line and the ground line while a selected slave unit (200.k) is operating in a high-power mode and the remaining slave units (200.i) are operating in the low-power mode; the slave units (200.i), determining a positioning voltage potential drop ( V i pos) across the power line and the ground line while the selected slave unit (200.k) of the plurality of slave units (200.1 to 200.n) is operating in the high-power mode; and the master unit, collecting relative voltage potential drops ( ΔV i) for each slave unit (200.i), wherein each relative voltage potential drop ( ΔV i) is based on the reference voltage potential drop V i ref and positioning voltage potential drop ( V i pos) measured by the respective slave unit (200.i); the master unit, determining relative positions of the plurality of slave units (200.1 to 200.n) based on the collected relative voltage potential drops ( ΔV i). the master unit, instructing each slave unit (200.i) to measure the reference voltage potential drop V i ref while each slave unit (200.i) is operating in a low-power mode; each slave unit (200.i), determining a reference voltage potential drop V i ref across the power line and the ground line while the slave units (200.i; 200.1 to 200.n) are operating in the low-power mode; the master unit, instructing each slave unit (200.i) to measure the positioning voltage potential drop ( V i pos) across the power line and the ground line while a selected slave unit (200.k) is operating in a high-power mode and the remaining slave units (200.i) are operating in the low-power mode; the slave units (200.i), determining a positioning voltage potential drop ( V i pos) across the power line and the ground line while the selected slave unit (200.k) of the plurality of slave units (200.1 to 200.n) is operating in the high-power mode; and the master unit, collecting relative voltage potential drops ( ΔV i) for each slave unit (200.i), wherein each relative voltage potential drop ( ΔV i) is based on the reference voltage potential drop V i ref and positioning voltage potential drop ( V i pos) measured by the respective slave unit (200.i); the master unit, determining relative positions of the plurality of slave units (200.1 to 200.n) based on the collected relative voltage potential drops ( ΔV i).