An inflatable air spoiler for the use with a vehicle to reduce wind resistance. A high frequency radio receiver receives echoes from the radar signal in which each echo represents a reflection of the radar signal from an object. A timing averaging circuit 10 is fed with clocks from a position on a forward route 111 of a direction-reversed clock propagation path, adapted for being fed with input clocks at its one end, and from a position on a return route 112 corresponding to the position on the forward route 111. The peeling blade, when used, is directly between the fingers and, therefore, can be guided in an extremely precise, handy and safe way. In another embodiment, a positive locking key prevents rotation of the inner ring relative to the adapter sleeve.