Procedures
If you would like to know a date on the Western (Gregorian) calendar from October 15, 1582 onward, you use Y for the last four digits of the year, M for the month, and D for the day.
If M < 3, Y’ = Y  1 (However, when Y = 0, Y’ = 9999) and M’ = M + 12. If M ≥ 3, then Y’ = Y and M’ = M.
By implementing the following process, if the position that you finally come to is 0, 1, …, 6, Wed, Thu,…, Tue is your desired day.
Supplement:
On the joints of the index, middle, and ring fingers on your left hand, place the following numbers in the 7 marked out positions. From the tip of your index finger: 0,1,2. From the tip of your middle finger: 3,4,5. On the tip of your ring finger: 6. For integers a,b, 0≤a<7, and 0≤b<7, the position bafter of a indicates position (a+b)%7. However, for integers c,d (d≠0), you divide c by d and write the remainder c%d. See also nafter.
A method to guess the day of the week of a specific date by calculation using fingers “Light”:
Step 1 
Hold position that corresponds to M’ (Table 1).


Step 2 
Shift the held position to 0after and count 1.

Step 3 
Shift the position to be held to 0after every time when 7 are added as long as the total number does not exceed D.

Step 4 
Shift the position to be held to 1after every time when 1 is added as long as the total number does not exceed D.

Step 5 
Shift the position to be held to 0after and count maximum factor of 400 within a range equal to Y'or less.

Step 6 
Shift the position to be held to 5after every time when 100 are added as long as the total number does not exceed Y'.

Step 7 
Shift the position to be held to 4after every time when 20 are added as long as the total number does not exceed Y'.

Step 8 
Shift the position to be held to 5after every time when 4 are added as long as the total number does not exceed Y'.

Step 9 
Shift the position to be held to 1after every time when 1 is added as long as the total number does not exceed Y'.

(End Process)
Table 1  
3  4  5  6  7  8  9  10  11  12  13  14 
0  3  5  1  3  6  2  4  0  2  5  1 