Patent ID: 8103461

Claim:
Method for determining the temporal position of a wave packet ( 31 ) in a flow measuring apparatus, in particular a spirometer, comprising: providing at least one transducer for sampling ( 94 , 95 ) the wave packet at a plurality of points in time, wherein a measured value is created at each point in time; providing a microprocessor for calculating a sum of products ( 43 , 54 , 55 , 63 , 64 ), wherein each product is calculated for a determined point in time from the plurality of points in time and each product is the product of a value of a compare function ( 44 , 53 , 56 , 61 , 62 ) at said determined point in time and the measured value at said determined point in time; and calculating ( 46 , 47 , 57 , 58 , 65 - 81 ) the temporal position of the wave packet from the sum of products, wherein the compare function is a sine function ( 56 ) from which a second sum of second products is calculated ( 54 ), wherein each second product is calculated for another determined point in time from the plurality of points in time and each second product is the product of a value of a cosine function ( 53 ) at said another determined point in time and the measured value at said determined point in time, and the temporal position of the wave packet is calculated as arc tangent function ( 57 ) of the quotient from the sum of products divided by the second sum of second products.