1. A method of pattern recognition comprising: producing an electrical signal related to a standard object of a type exhibiting a pattern to be recognized; storing characteristics of said electrical signal in a pattern recognition system to produce a stored standard signal; setting a predetermined value A for determining whether or not an electrical signal contains characteristics sufficiently close to said stored standard signal to be judged to be the same as said standard object; producing a second electrical signal related to an object being inspected; determining a difference between said second electrical signal and said stored standard signal; outputting a match electrical signal indicating that said second electrical signal represents an object exhibiting said pattern if said difference differs from said predetermined value A by less than a threshold value; outputting a non-match electrical signal indicating that said second electrical signal does not represent an object exhibiting said pattern if said difference differs from said predetermined value A by more than said threshold value; increasing and decreasing a value of said predetermined value A with time in accordance with said difference; and continuing the above steps of producing, determining and outputting for each object being inspected whereby said threshold A is varied according to changing external conditions.