German term (edited): buchungsz�hler

Without more context, I can't say if it's variation 1 or 2 as per above. But I worked for years for a German software company specialized in airline ticketing systems and we used the above-mentioned. The 1st if in reference to actual airline reservations, the 2nd if referring to debits and credits posted to various bookkeeping accounts. If you want, send me a mail with more context and I can tell you exactly. Good luck!!!