The lunar-eclipse instructions of 1577 and the longitude of the Indies

In the same packet as the famous 1577 questionnaire, Spain sent the Americas a second printed sheet almost nobody reads: instructions for observing eclipses of the moon in order to fix latitude and longitude. It was reprinted for each eclipse year, and it worked at least well enough that by February 1578 a cosmographer was asking the Council of the Indies for the observations that had come in from New Spain "porque hace mucho al caso para las longitudes".