a method for determining a usage fee for a digital photolithography system is provided . the method is implemented as a computer program in a computer system used with the digital photolithography system . a digital mask is first received into the computer system , the digital mask being a source of pattern information for a digital pattern generator . whenever a portion of the digital mask is transferred to the digital pattern generator , the transfer is detected and a counter is updated , accordingly . this is done only if the first digital mask is new . the usage fee can thereby be determined from the counter .