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 (except that if Y = 0, Y' = 9999). If M ≥ 3, Y' = Y.
By implementing the following process, if the position that you finally come to is 0, 1, …, 6, Wed, Thu,…, Tue is your desired day. However, for integers a,b (b≠0), you divide a by b and write the remainder a%b.
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. See also nafter.
A method to guess the day of the week of a specific date by calculation using fingers “Pro”:
Step 1 
Hold on 0.


Step 2 
Shift the held position to nafter that n corresponds to M (Table 1) and count M.

Step 3 
Shift the held position to (D1)%7after and count D.

Step 4 
Shift the held position to 0after and count maximum factor of 400 within a range equal to Y'or less.

Step 5 
Shift the position to be held to 1after every time when 300 are added as long as the total number does not exceed Y'.

Step 6 
Shift the position to be held to 3after every time when 200 are added as long as the total number does not exceed Y'.

Step 7 
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 8 
Shift the position to be held to 2after every time when 80 are added as long as the total number does not exceed Y'.

Step 9 
Shift the position to be held to 5after every time when 60 are added as long as the total number does not exceed Y'.

Step 10 
Shift the position to be held to 1after every time when 40 are added as long as the total number does not exceed Y'.

Step 11 
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 12 
Shift the position to be held to 3after every time when 8 are added as long as the total number does not exceed Y'.

Step 13 
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 14 
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  
1  2  3  4  5  6  7  8  9  10  11  12 
5  1  0  3  5  1  3  6  2  4  0  2 