title: R/exams: implement only six boxes for the registration number
body: <p>I am working with with the <code>exams2nops</code> function of the R/exams package. Since the student's registration number of my university includes only six numbers, I tried to adjust the <code>reglength</code> option (usually minimum 7) in the <code>exams2nops</code> function as well as the <code>nops_scan</code> and <code>nops_eval</code> functions. Creating only 6 boxes was not the problem but the evaluation process is more sensitive to scan quality and contrast problems. If the quality of the scans is perfect, the evaluation works (almost) perfectly with my adjustments but whenever there is a slight lack of quality in the scans, I have to enter some/all registration numbers manually while the interactive process. Since my adjustments were only improvised and not really elegant because I do not understand every part of the source code, I am searching for a more stable solution now. Is there any way to reduce the registration number to six boxes without having problems in the evaluation process afterwards?</p>