You young ones have it easy - back before the metric system every country had their own system of measurement, and in fragmented places like Germany, each canton had its own foot or yard. We had it tough caving back then. Saying that a cave was a mile long was a very different thing to a Prussian as opposed to a Castillian, with the Prussian having nine miles to the Castillian's one.
I remember trying to draw up Gr?neschweinh?hle from Karsten van Adelstropp's notes in 1773 - of course you might expect that he would have measured the place in Klafters, but the only tape he could get a hold of was an old miners measuring chain which used Lachters. So, to make things easier for me, Karsten converted all the measurements to Swabian Feet (since I was in Grenoble at the time, using the pre-revolutionary French measurement of the Toise (seven Swabian feet was exactly equal to one Toise, therefore easier to convert than the more commonly used Silesian Foot (which went into one Toise 6 and three-fifths times))). However, I assumed that Karsten, being a Bavarian, would use the Bayruthean Foot (seven and one sixth to one toise), so I converted all of his measurements to the French system, which meant that every measurement was out by one 'Pied Royale' in every seven Toise. To make matters worse, Karsten wrote to me that winter to tell me that he'd discovered the measuring chain he'd used was made in Darmstadt, so it was probably based on the Hessian Lachter, which was one Zoll (about an inch), longer than the Bohemian Lachter that he though it was. At first I tried to correct the scales by rounding up or down each Pied Royale to the nearest Pouce, and then converting the lot to Amsterdam Feet, using the table at the back of and old copy of Zijkermeyer's Mercantile Almanac. But this I discovered pre-dated the Dutch measurement standardisation of 1767, so I scrapped that, and used a log table to convert all the measurements to decimal fractions of the Swiss Mile (on account of the Swiss Mile being exactly equal to 468 Toise, and therefore possible to use a base of 4.5 to calculate the exponent (or vice versa, which was why distances from Lucerne and Geneva to French towns and cities were often given in duodecimal fractions of the Toise).
At the end of all of this the centreline was plotted on a linen sheet about two (Scottish) fathoms across, with scale bars for Dutch Roeden, Thuringinan feet, French (i.e. Parisian) Miles and Castillian Yards. The engraver nearly had a fit when he saw this, but I managed to use a Camera Obscura to reduce it down to fit onto one Double Demy sheet, and we got the survey printed in time for that years Journale Francaise d'Geographie.
Another problem was disputed measurements - in 1781 the Belgians (Part of the Spanish Netherlands back then) claimed to have the deepest cave in the world (Grotte d'Agositina) at a depth of 88 (Dutch Standardised) Roeden. The Swiss claimed that Brutenh?hle was deeper at 7845 Helvetican Inches, claiming that the Belgians were (somewhat sneakily) using the Pre-standardisation Rotterdam Roede, giving it an actual depth of 79 (Dutch Standardised) Roeden (about 23 metres in modern parlance). As it turned out, the Swiss were correct on the measurement side of things, but as we now know, the Grotte d'Agositina was actually a medieval soil mine, something that was hard to make out with the poor lighting that we had back then.
