 However, the design creates idle currents in the armature, which result in losses, and on larger machines, where interpoles are required, each interpole must be fitted with two coils, one for each of the brush circuits.Tustin argues that there is little advantage of the Magnicon over the Metadyne for smaller machines, and for larger machines, which require interpoles to be fitted, insufficient analysis has been carried out to make a judgement.Metadynes have been used to control the aiming of large guns and for speed control in electric trains, in particular the London Underground O and P Stock.