Patent ID: 7408838

Claim:
A planimeter comprising: A) a housing; B) a pair of distance sensors secured to the housing, each of which is associated with a different sensor region and includes: i) a radiation transmitter operable to send radiation into the sensor region associated with the distance sensor that includes that distance sensor; and ii) a radiation receiver that is disposed in the housing and generates in response to echo radiation reflected from the sensor region associated with that distance sensor a sensor output dependent on that echo radiation; and C) computation circuitry contained in the housing and so arranged as to: i) determine a respective two-dimensional position of the housing, for each of a sequence of locations of the housing, from the difference between times of radiation transmission and reception that occur while the housing is disposed at that location; ii) store the sequence of two-dimensional positions thereby determined; iii) compute at least one length from the difference between a pair of such two-dimensional positions in that sequence; and iv) generate an output representative of a quantity that depends on at least one such length.