Mathematical_Recreations-Kraitchik-2e

116 Mathematical Recreations
intersection of this inner ring and a radius. (If the month is
January or February, use the preceding year.) Draw a line
between these two points on the inner ring; if they coincide,
then draw a tangent to the inner ring. (If they coincide on
Saturday, then Saturday is the week day sought.)
4. Now find the point where the Saturday radius cuts the
inner ring, and through this Saturday point draw a line parallel
to the line just drawn. The two lines may coincide; in
any case, the line will meet the inner ring at some radius-ring
intersection. The week day on this latter radius is the week
day of the Date with which we began. If the last line drawn
is tangent to the inner ring at the Saturday intersection,
then the day is Saturday.
To help in locating such details as Date of the month,
Year number and Century number, a table has been prepared.
If there is any difficulty in locating a Year, say 45,
it may be looked up in the detail-finding table, which will
show that Year 45 is at the intersection of the inner ring and
the Saturday radius.