日本語版 | Java Applet Instructions / List of Programs
F - T = d shows how many days passed from the date in "From" row to that in "To" row. (Suppose the date in "From" is the 0-th day. Then it calculates the integer D such that the date in "To" row is the D-th day.)
F + D = t shows the date when D days passed from the date in "From" row. (That is, it calculates the D-th day.) Here the integer D is given by "Days" and may be negative.