Why does my weight go up and down when I am on a diet? Also, weigh in tips.

It's frustrating to get big ups and downs of your pounds day to day and even hour by hour.  About six pounds a day, mostly water, goes in and out.  See picture showing my 90 day weigh-ins.  The trend-line is steadybut the road is bumpy.

We measure pounds to indirectly measure calories.  3500 calories skipped is a pound of fat lost. (Roughly accurate).    But what I eat and drink and pee and breathe out are also pounds, mostly water, and not pounds of flesh.  If my diet is consistent, my daily flesh loss will be consistent.

My goal is to lose one pound a week or 2-1/4 ounces per day (Equivalent to the weight of six cherries every day).  It turns out that the amount of stuff (mostly water) that goes in and out of my body every day is 40 times bigger than that.  No wonder it's hard to get consistent results every day.

Here's a graphic.  Below it is my data from measuring one day.  The numbers are a fair fit.  (I think "metabolism" refers to some of your fat being taken out of reserves and put into the daily mix for activity.)

I weighed everything I could for one day and compared it to an online graphic.  Here's the information: (A millileter of food and drink is pretty close in weight to one gram.)

IN:
Food by weight:  1180 grams
Beverages by weight:  1630 grams.
Total:  2810 grams or  6 pounds and 3 ounces.

OUT
Urine by weight:  1780 grams
The brown stuff:  150 grams.
Total:   1930 grams or  4 lbs 4 ounces.

My beginning weight:  196.6 lbs.
My weight 24 hours later:  196.2 lbs.
The obvious IN and OUT don't balance and yet my weight stayed about the same.
Poo is a much smaller factor than pee and the rest of the loss must be in moisture that my damp breath and sweaty skin gave out.   Besides  that, extra salty dishes will temoprarily bump your weight as water is retained.  (You'll see marks where your socks imprint the skin).  Cut your salt back for a couple days if you want a great weigh-in.

And herewith, a couple weigh-in tips.
-The wise ones tell us to weigh just once a week and they are probably right since there is so much intraday variation.  On the other hand, if you don't like that, weigh as often as you are curious.
-If you use something several times a day like butter or liquor, just weigh it once, at the beginning and the end of the day.  I used to like a tiny sip of Drambuie at regular intervals and it added up to to a lot of calories, even though it was just a teaspoon at a time and "not worth weighing".  For a while I weighed the bottle morning and night.  Then, armed with the new information, cut the Drambuie from my diet.
-Your lowest weight of the day will almost certainly be when you get up in the morning, after having peed and having breathed out a lot of moisture.  This could be two or three pounds every night.
-In case you wonder, your towel picks up about a third of a cup of water (80 grams) from drying your skin.  People with long hair will get a larger number.
-If you like to weigh early and weigh often, take the things you usually wear around the house during the day (in my case this excluded shoes but included a cell phone, belt,  and long pants) and weigh them on a kitchen scale.  In my case, this worked out to 3.0 pounds, less if I wore shorts.  Subtract that figure to get your naked-as-the-day-you-were-born number.
-Your scale isn't perfectly accurate.  It's hard to read a spring operated scale closer than a pound.  An electronic scale may give a couple readings the same but ten minutes later give a different reading, say .4 or .6 pounds up or down.  An e-scale that has been bumped may need to recalibrate.  This means the second reading will be more accurate than the first.  UPDATE:  We changed from sculptured floor tile to smooth tile and the digital scale began to be remarkably consistent. If the floor isn't really flat, you are probably getting some false readings.