Weekday
-
Weekday
- Day of the week for any date since September 14, 1752
Source: HP-45 Applications Book (HP 00045-90320 Rev. B Reorder 00045-66001, Dec 1974)
d = day of month
m = month, with January and February beeing the 13th and 14th months of the previous year.
y = year (4 digits)
Weekday = (d + n1 + n2 - n3 + n4) mod 7
where
n1 = Int(13⁄5·(m + 1))
n2 = Int(5⁄4·y)
n3 = Int(y⁄100)
n4 = Int(y⁄400)
Int is "integer part of".
Output is read as follows:
0 - Saturday
1 - Sunday
2 - Monday
3 - Tuesday
4 - Wednesday
5 - Thursday
6 - Friday
Example:
On what day was February 29, 1972?
Answer:
Tuesday (d=29, m=2, y=1972)
| LINE | DATA | OPERATIONS | DISPLAY | REMARKS |
|---|---|---|---|---|
| 1 | d | ENTER |
||
| 2 | m | ENTER |
||
| 3 | y |
 STO A R↓ ENTER
|
||
| 4 |
1/x 0 . 5 +
|
|||
| 5 |
 INTG 6'IP
|
f | f is 1 if January or February, otherwise 0 | |
| 6 |
STO - A
|
January and February beeing the 13th | ||
| 7 |
1 2 × +
|
and 14th months of the previous year | ||
| 8 |
1 + 1 3 ×
|
|||
| 9 |
5 ÷
|
E1 | Let e1=integer part of E1 | |
| 10 |
INTG 6'IP
|
e1 | ||
| 11 |
+ x≶ A ENTER
|
|||
| 12 |
ENTER ENTER 5 × 4
|
|||
| 13 | ÷ |
E2 | Let e2=integer part of E2 | |
| 14 |
INTG 6'IP
|
e2 | ||
| 15 |
RCL A +
|
For 20th century date, | ||
| go to 23 | ||||
| 16 |
STO A R↓ 1
|
|||
| 17 |
0 0 ÷
|
E3 | Let e3=integer part of E3 | |
| 18 |
INTG 6'IP
|
e3 | ||
| 19 |
STO - A R↓
|
|||
| 20 |
4 0 0 ÷
|
E4 | Let e4=integer part of E4 | |
| 21 |
INTG 6'IP
|
e4 | ||
| 22 |
RCL A +
|
Go to 24 | ||
| 23 |
6 +
|
|||
| 24 |
7 RMDR
|
w | Remainder part of the integer division by 7 |