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The Magic Cafe Forum Index » » Magical equations » » Calculating the Number of Days Between Two Days (0 Likes) Printer Friendly Version

Edmark Law
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Hong Kong
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Is there a known method exists that lets you mentally calculate the number of days between two dates? I am not asking how it's done, I just want to know if there are any sources for this kind of calculation. I am fimiliar with many of the "lightning calculation" techniques and also regularly performing them. So, I have read many books about the subject. However, it seems that I can't find any references for this. Any suggestions will be appreciated.
hcs
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To calculate mentally the number of days in a year for a given date is known since Dionysius Exiguus.

I give an English source in my Encyclopedia of weekday calculation on p. 48 "[2] Thomas Harrington: „The Magic of Memory: Phonetic Mnemonics”, “The numbers of the days throughout the year” and “date to day”, p. 13-15; Lybrary.com, 2007".
Subtract the numbers of two days (for two dates in a year) gives one the result asked for.
DinY = 30(M - 1) + M' + D
Scott Cram
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Here are a couple of online links that may help, as well:

http://powertoolsandtips.blogspot.com/20......nce.html

http://powertoolsandtips.blogspot.com/20......orm.html

The Thomas Harrington approach mentioned by Hans Solka is good, as he uses some very simple mnemonics. However, once you realize that each month is approximately 30 days, you know your multiples of 30 up to 11 (0, 30, 60, 90, 120, 150, 180, 210, 240, 270, 300, 330), and get familiar with the actual number of days preceding each month, you'll find that you don't need the mnemonics as much anymore.

Just for fun, here's a polynomial equation that generates the number of days before any month, where the month is given as a number 1 (January) through 12 (December). I even worked out a version for leap years!
Edmark Law
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Quote:
On Jan 18, 2015, hcs wrote:
To calculate mentally the number of days in a year for a given date is known since Dionysius Exiguus.

I give an English source in my Encyclopedia of weekday calculation on p. 48 "[2] Thomas Harrington: „The Magic of Memory: Phonetic Mnemonics”, “The numbers of the days throughout the year” and “date to day”, p. 13-15; Lybrary.com, 2007".
Subtract the numbers of two days (for two dates in a year) gives one the result asked for.
DinY = 30(M - 1) + M' + D


Thanks for your reply. I'll definitely check it out.

Quote:
On Jan 19, 2015, Scott Cram wrote:
Here are a couple of online links that may help, as well:

http://powertoolsandtips.blogspot.com/20......nce.html

http://powertoolsandtips.blogspot.com/20......orm.html

The Thomas Harrington approach mentioned by Hans Solka is good, as he uses some very simple mnemonics. However, once you realize that each month is approximately 30 days, you know your multiples of 30 up to 11 (0, 30, 60, 90, 120, 150, 180, 210, 240, 270, 300, 330), and get familiar with the actual number of days preceding each month, you'll find that you don't need the mnemonics as much anymore.

Just for fun, here's a polynomial equation that generates the number of days before any month, where the month is given as a number 1 (January) through 12 (December). I even worked out a version for leap years!


Thanks, that helps a lot. Btw, I really like your blog. Keep up the good work.
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