Footnote 71
Supp. Prop., §45. Here the author enters a little more into particulars.  If the mean motion be required for the year 1400, 3 years later than the starting-point, look for 3 in the table of expanse years, and add the result to the number already corresponding to the `root', which is calculated for the last day of December, 1397.  Allow for months and days afterwards.  For a date earlier than 1397 the process is just reversed, involving subtraction instead of addition.