# I weighed 199 pounds last night.

**URL:** <https://boards.straightdope.com/t/i-weighed-199-pounds-last-night/621299>\
**Category:** Miscellaneous and Personal Stuff I Must Share\
**Created:** [May 8, 2012, 5:34pm UTC](https://boards.straightdope.com/t/i-weighed-199-pounds-last-night/621299 "2012-05-08T17:34:32Z")\
**Posts on this page:** 2\
**Page:** 2

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**Author:** ![Mean\_Mr.Mustard](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mean_mr.mustard/32/3865_2.png) [@Mean\_Mr.Mustard](https://boards.straightdope.com/u/Mean_Mr.Mustard)\
**Post date:** [May 14, 2012, 1:44pm UTC](https://boards.straightdope.com/t/i-weighed-199-pounds-last-night/621299/21 "2012-05-14T13:44:09Z")

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Hey Hari - Could you please eyeball these hypothetical numbers and see if I have the idea? I would appreciate it!

mmm  
12-05-14…278.4  
12-05-15…276.0…278.16  
12-05-16…275.2…278.08  
12-05-17…276.4…278.20

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**Author:** ![Hari\_Seldon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hari_seldon/32/5173_2.png) [@Hari\_Seldon](https://boards.straightdope.com/u/Hari_Seldon)\
**Post date:** [May 14, 2012, 7:33pm UTC](https://boards.straightdope.com/t/i-weighed-199-pounds-last-night/621299/22 "2012-05-14T19:33:01Z")

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Not quite  
12-05-14…278.4  
12-05-15…276.0…278.16 That’s correct. Subtract 10% of 278.4 - 276.0 or .24  
12-05-16…275.2…278.08 That’s not correct. First, the rounded previous average is 278.2. 10% of the difference between that an 275.2 is .30, so that should be 277.86, rounded 277.9.  
12-05-17…276.4…278.20 Continuing in the same way, 277.9 - 276.4 = 1.5 so you should subtract 10% of that or .15 from the previous average of 277.86 to get 277.71. For the next one, you would use 277.1. Note that the second decimal place is meaningless but I use it to control round-off errors. Technically, I believe it is called a guard digit.

If you are interested, I will tell you that this method produces an average of the current day’s weight, 90% of the previous day’s weight, 81% (.9^2 = .81) of the second previous day’s, 72.9% of the third previous day’s and so on, the influence of each day declining by 10% over its previous influence. By 20 days it is down to about 10% and is more-or-less negligible after that.

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