City Inspectors
An important source of income for the cities in the Republic was the excise taxes (accijns), on goods brought into each city: beer, which was consumed by adults and children in the absence of clean drinking water, as well as wine, spirits, vegetable and fish oils, and other liquids, meat, peat, salt, soap, woolen cloth and grain. Almost all of the Republic's grain for bread (and beer) was imported from the Baltic breadbasket.
A long and ever-changing list of goods were taxed at ever-changing rates. For some goods, it was just a matter of weighing them at the Waag. For other goods, specifically liquid in barrels, this was more complicated because barrels were not standardized, the sides were curved, and for the liquid, the quality could be more important than the quantity. The men who did this job were called gaugers or assessor (peilder) after the measuring stick or gauging rod (peilstok) they inserted into the barrels.
The person who measured the content of wine vats was called a wine gauger (wijnroeier), a job Leeuwenhoek performed for the city for twenty years.
In the world before standards, when each Dutch city was its own little economy with its own standards and monetary system, the wine gaugers had to be trusted to standardize within a city's ecomomy. The arithmetic for measuring the volume of curved spaces was not difficult, but the computational skills were not common, either.
After the wijnroeier measured something, it could then be fairly taxed and confidently subdivided, combined, bought, and sold, now and in the future. As were many officials whose jobs involved a degree of trust, they were sworn in (gesworen and beëedigde). What an importer thought he had, and what the shipment's documents said he had, was not as important as what the wine gauger measured that he had.
In 1679, Leeuwenhoek was selected for this important position, and held it for the rest of his life. Each city organized this task differently and gave the functions different names and compensated it differently.
According to the sixth Keurboek der Stad Delft/Delft City Bylaws, folio 207, the wine gaugers swore to this oath: