My mother called the Dutch Military and Armory Museum in Delft. A researcher there looked up the units of measure in a book about the army in the post-napoleontic era. It turns out that during Napoleon's reign all units of measure were standarized in what is now known as the metric system. However, the old names were kept for a while. It wasn't until later that the names 'meter' or 'kilogram' came into use.
This means that the "el" (previously ranging from 68 cm to 91 cm depending on the province or the city) was redefined as having the length of 1 meter. The "el" was subdivided into 10 palms (approx. the width of a handpalm), so each palm is 10 centimeters. The palm itself was subdivided into 10 'duim' (thumb, 1 centimeter) or in 100 'streep' (stripe, 1 millimeter). So Ulbe's length was 1 el 705 st. or 1 meter 70.5 centimeter or 5 foot 7 inches in the American system. So even by today's standards he wouldn't have been real short, and in those days he probably was quite tall.
A little bit more about the units of measure. My mother had guessed before that 'st.' would be a 'streep' because she had heard carpenters use that phrase ("I have to take two stripes off that door", meaning that they have to shave some wood off). So these old names are still in use albeit in a specialized profession. In fact, the dutch words 'pond' (metric pound, 500 grams) and 'ons' (metric ounce, 100 grams) are used by everyone even though they cannot be used in official trade like supermarket ads.