That webpage sums up the concepts of the lunar and solar measuring pretty well. Its measurements must have been crucial for the farmer/settlers in the past, if we also consider some/many megalithic monuments (callanish, recumbents, etc) to be alligned on the moon. The sun is fairly easy to measure from a fixed position during the year, and to mark its movements easy. The harder part was the moon.
In terms of calendars, the pre-christian calendar may have been a 13 month long year, ie one with lunar months of 28 days each, with one day extra every year. That extra day may have been the one devoted to New Year.