as used by rfid devices in all embodiments of this present application the user has limited degrees of freedom when placing devices therefore it may be advantageous to indicate these constraints to the user such indications may be done in a variety of ways for example for chargers with placement restrictions indicating the correct device position by means of outlining of the coil area filling or patterning the active coil area for chargers with rotational restrictions indicating the correct device rotation by means of the indications may be rendered in any number of media for example printing ink perhaps of a particular colour raising or lowering the charger surface overall shape of the charger or part of it some examples of possible indications are shown in fig1 which fig1 a shows a printed or raised outline of two devices for chargers which have no degrees of freedom fig1 b shows a printed or raised arrow on both the charger and the device for chargers with 2 translational but not rotational degrees of freedom fig1 c shows similar to 12 b but with striped indication instead of arrows fig1 d shows a u201c target u201d of concentric circles on both charger and device for chargers with only a rotational degree of freedom fig1 e shows a charger with one circular translational degree of freedom designed such that the active area of the charger is obvious from its form prior art such as u s pat no 5 952 814 philips phone charger with interlock describes how the casing of charger may be made to match the internal shape of the charger thus allowing for accurate alignment of the primary and.