Apparatus for cutting the leading and trailing edges of an opaque sheet angling initially at an offset angle with respect to a cutting blade includes a pair of light sources and a pair of light sensors opposite said light sources. An opaque sheet to be cut is moved at right angles to a line extending between said pairs of light source and sensors to bring said article edges to and past said pairs of light sources and sensors. The sensors produce article edge angle indicating signals which indicate the time difference each edge reaches said pair of sensors. Means are provided responsive to said signals which adjust the blade angle to be parallel to each article edge so the blade cuts parallel to each edge. The angle indicating could be signals which are a direct measure of the difference in times each edge reaches the sensors. However, they are preferably derived from sensors measuring the relative amounts of light at a snapshot time passing through slots partially covered to different degrees by the sheet edge portion involved when the edge being measured is at an angle to said line.