Navigation technique for detecting movement of navigation sensors relative to an object

A method of operating a detecting device comprising the steps of:

• generating electrical signals, representative of a position, by a navigation sensor, said electrical signals providing sequential frames of navigational information at time intervals;
• storing a first frame of navigational information generated at time N in a first memory buffer;
• storing successive frames of navigational information, subsequent to said first frame, in a second memory buffer;
• comparing a current frame of navigational information generated at time M to a previous frame, immediately preceding said current frame, stored in said second memory buffer and generating a first displacement value representative of a difference between said current frame and said frame of navigational information immediately preceding said current frame;
• processing data based on said first displacement value to take into account movement of said navigation sensor relative to a reference when processing said data;
• comparing a current frame of navigational information generated at time T, subsequent to time M, to said first frame of navigational information stored in said first memory buffer and generating a second displacement value representative of a difference between said current frame generated at time T and said first frame;
• processing data based on said second displacement value so that said data is not affected by accumulated errors from other displacement values;
• and
• storing a current frame of navigational information generated at time V, subsequent to time T, in said first memory buffer for comparison to a later frame of navigational information.