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:

Ick belove ende sweere, dat ick als wijnroeier de wijnes en de andere waren, die mij om te roeien voorkomen sullen opregtelijk ende naar mijn beste wetenschap conform de kunst van het wijnroeies sal roeien ende meten ... ende dat ick voorts in alles sal doen dat een goed oprecht wijnroeier schuldich is te doen.
"I promise and swear, that I, as gauger for wines and other commodities that will offer themselves for me to gauge, truly and with my best learning in accordance with the art of wine gauging will gauge and measure ... and that I moreover in everything will do what a sincere wine gauger is obliged to do."
The wine gauger was also called the ijkmeester, wijnverlater, wijntapper, and collecteur der wijnen. In the notarized statemnt of accounts, Leeuwenhoek is sometimes referred to as a peijlder. The image below shows some measuring sticks from the mid-1700's a little after Leeuwenhoek's time, but the design was the same: a rod with evenly spaced marks.
The Delft bylaws also say:
Item sullen alle vaeten die binnen de Stadt gevult sullen werden, van acht tot veertig stoopen voor de eerste reijse eer d'selve uut de kelder sullen gaen nootsaeckelijck moeten gewatericht ende daernae gebrant werden met de letter D (= Delft) deur den roeier selffs in persoon, sonder dat hij daertoe ijemant anders sal mogen gebruijcken.
"Likewise, all barrels to be filled with the City, from eight to forty stoups, will for the first time out of the cellar need to be made watertight and after that branded with the letter D by the gauger in person, without his being permitted to use anyone else for that purpose."
ijken = calibrate, verify
verlaten = to draw wine from one barrel to another
peil = gauge, level