The Revision Books were used for about 10 years and then replaced by new books. The clerks went round every couple of years and updated the records. They used a different coloured ink for each year’s visit. So in the example you have given, John Meaghan was replaced by Anne Treanor in 1901 (red ink). In 1908 (purple ink) the plot was renumbered slightly. What had been plots 27A & 27B was combined as 27AB. The numbers 6869 in red at the extreme left are the number of the amendment. Similar numbers, in a rising sequence, appear against every amendment made in that townland.