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Claim 1

APPARATUS FOR INDICATING THE CONCENTRATION OF RECURRING SURFACE CONTOURS CAUSED BY THE THREAD ARRANGEMENT IN A PIECE OF FABRIC, SAID APPARATUS COMPRISING MEANS FOR GENERATING FIRST SIGNALS REPRESENTATIVE OF THE MOVEMENT OF A PIECE OF FABRIC IN A GIVEN DIRECTION PAST A GIVEN POINT, A PHOTOSENSITIVE ELEMENT MOUNTED ABOVE SAID POINT AND ORIENTED WITH ITS LIGHT SENSITIVE SURFACE FACING SAID POINT, A LIGHT SOURCE ALSO MOUNTED ABOVE SAID POINT, MEANS FOR CONCENTRATING LIGHT ENERGY FROM SAID LIGHT SOURCE INTO A NARROW BEAM AND FOR DIRECTING SAID BEAM DOWN AGAINST THE MOVING FABRIC AT SAID GIVEN POINT, SAID LIGHT CONCENTRATING MEANS BEING OF SUCH CONSTRUCTION THAT IT EFFECTIVELY RESTRICTS THE CROSS-SECTIONAL DIMENSION OF SAID BEAM IN THE DIRECTION OF FABRIC MOVEMENT TO AN AMOUNT SUBSTANTIALLY LESS THAN THE CORRESPONDING DISTANCE IN THE SAME DIRECTION ACROSS THE INDIVIDUAL SURFACE CONTOURS ON THE FABRIC SO THAT THE BEAM WILL STRIKE THE FABRIC AT DIFFERENT ANGLES AS THE CONTOURS ON THE FABRIC MOVE PAST SAID GIVEN POINT, AND BECAUSE OF THIS CHANGE IN ITS ANGLE OF INCIDENCE, THE BEAM WILL BE REFLECTED SUCCESSIVELY IN DIFFERENT DIRECTIONS AND THUS WILL BE SWUNG INTO AND OUT OF THE LINE OF SIGHT OF SAID PHOTOSENSITIVE ELEMENT, MEANS FOR GENERATING SECOND SIGNALS IN RESPONSE TO THE REFLECTION OF SAID BEAM ONTO SAID LIGHT SENSITIVE SURFACE AND MEANS FOR INDICATING THE RATIO BETWEEN SAID SECOND AND FIRST SIGNALS.