Are you asking about water weight simply from what you drink every day while
maintaining a LC woe?  Who cares?  Just get on the scale at the same time
everyday and forget about it.

Or, are you asking about the additional water weight your body will hold in
your muscle and liver when you consume a large amount of carbs after being
on LC for a fair amount of time?  That is a more real question, IMO, because
as you graduatelly increase your carb intake you might find yourself
approaching the higher weight.  Or, if you should carb up your wieght will
increase due to holding water. So, if while on low carb you weigh X, then it
is very possible that when not on LC you could weigh X+Y, when Y is the
weight of the water held in your muscles and liver.   I consider both of
those to be real, meaningful numbers.

IMHO if you weigh yourself multiple times a day and get various
numbers, the lowest one is "you" and the rest of the weight is
"stuff".  A NASA study found that about 13 lbs of food and water goes
through the average adult male astronaut every day, so in theory this
is the amount by which your weight can vary each day.

This is why I graph my weights (I only weigh once a day though).  With
a long term graph, you can ignore the individual measurements and see
the long term trends.

http://www.delorie.com/health/ - get the weight print-a-chart.

Example of seeing trends behind the dots:
http://www.delorie.com/health/20030724-chart.png

Your real weight was 245 in the morning.  Then your real weight was 251
in the afternoon.  The fluctuation depends mostly on what you are
drinking and eating during the time interval between weighings.  The
food flowing through your ailementary canal has mass.  Sometimes you'll
have more in you then other times.  The liquids you drink will affect
your weight as well as your kidneys remove any excess.

Fat gains or losses in your body will not cause the weight fluctuation
of 6 pounds in 12 hours.

Lean Body Mass gains or losses in your body will not cause the weight
fluctuation of 6 pounds in 12 hours.

As you've noticed, body weight can vary quite a bit from day to day.  Most
folks who track their weight regularly find that weighing first thing in the
morning, after relieving oneself, provides a consistent number.  This also
tends to be the lowest reading of the day.

As others have noted, it's the long term trend that's most important.  So,
don't get too upset if you see a one-day "gain" of 2-4 lbs.  Likewise, don't
think you're doing great just because you see a one-day "loss" of similar
magnitude.

For the compulsive, or the scientifically inclined, one can calculate a
"moving average" weight using Excel, or other software.  This is a good way
of filtering out the daily ups and downs, and is probably more
representative of your "real" weight than any single measurement.

According to research conducted by the National Weight Control Registry,
"frequent weighing" is one of the behaviors associated with successful
weight loss.  I'm under the impression that most of their research
participants (folks who have lost around 60 lbs, on average, and kept it off
for at least 1 year) weigh themselves once per day, or thereabouts.

First thing in the morning. The rest is you plus whatever you've eaten or
drunk; that shouldn't count until you've had a chance to metabolise it.

Nicky.

I don't have an answer, but you're not alone.  I can weigh myself at the
same time everyday and find that I can vary up to a couple/few pounds.  Over
the course of a day, I've found variances as high as 5 pounds.  It used to
bother me, but I'm used to it now and as long as my belt keeps shrinking,
I'm happy.  :)

Mark

if you MUST weigh, i recommend daily, and then give yourself a
weekly average.
i measure with the size of my jeans.

The answer to your question is very simple.
You weight 245 to 251 lbs.
So, when you weight 240 to 246 lbs, you have lost 5 lbs.

The whole purpose of the scale is to let you know the gain/loss of your weight
in similar conditions.

=>
=>
=> Probably does not matter much. But there has been much discussion on
=>"water weight" and so on, especially during the initial period of lowcarb.
=>
=> But when you bounce 6 or 7 pounds a day, it is beginning to make no sense.
=>
=> If someone can vary as much as 6 or 7 pounds a day it becomes suspicious.
=>Is it the scale? I had it tested and it's a new Tanita. Checked against the
=>doctor's office. All good. My wife is consistently weighs in within .5
=>pounds. Each day.
=>
=> Ok. So I do drink a lot of water. Probably not enough, but what I call a
=>lot. 60 to 80 oz a day. (I think. Had not measured.)
=>
=> So the question is - you weigh between 245 and 251 lbs. What is your REAL
=>weight?  the first of the morning 245, or the late afternoon 251?
=>
=> Before the avalanche  - yes I know one should not obsess with weighing too
=>many times. Once a week is preferred, by my humble research. But even then,
=>how can one know? Gotto arrive at your goal and stay there 2 years before
=>you stabilize?
=>
=> Let it rip..
=>__
=>    Best Regards,
=>
=>                 Steve
=>
=>Tout est per·du fors l'hon·neur

I like to weigh before going to bed and the again after a long nights
sleep.  I lose 2 or 3 pounds doing that every day<g>.

I suppose you breate out a lot of water vapor overnight and maybe
perspire/evaporate some more moisture.   But my very lowest is after
I sleep for 10 hours.

dk

Now you're playing disbelief games *because* you've just
seen the hard evidence that statements about water retention
swing are actually true.  What's the sense in disbelieving
what you've just seen happen in yourself?

Of course water retention makes sense.  Stuff happens and
one day is different from the next.  The body stores carbs
dissolved in water so if you eat enough to store some
there is a bounce up.  Salt same deal.  New exercise
program same deal.  Slow to digest meal and more of it is
still in there.  You name it when it comes to reasons for
retention.

Why suspicious?  Because it's completely standard and
common?  Or because you don't *want* to believe the fact?
Ah, that's it, isn't it.  You don't like the reality
that you have seen so you're trying to work yourself into
denial by explaining it away.  Doesn't work that way.
Retention swing is real.

Scales do vary some.  Usually less than retention swing.

All good as in the same amount of swing, check.

Okay, so her swing is smaller than yours.  Shrug.
People are different.

Your weight is your most recent new low as long as
you have stayed on-plan enough to enusure
that you have not stored any new fat.

BZZZT!  Weighing within the same day is a way to lie to
yourself for the exclusive purpose of self sabotage.  Any
later weighings within the same day have no meaning
whatsoever.  It didn't happen as far as actual reality is
concerned.  Get off the fricken scale you self sabotager!

No you do NOT know that.  If you knew it you would not
be doing self sabotage by stepping on the scale so much
that you have begun to question what you actually see
happening.  You know, your lost weight.  Don't do
stuff to trash that.  Like multiple weighings per day
for no reason except to distract you from the reality
of your loss.

Come on.  A new low is a new low.  Retention swing above
your most recent new low is irrelevant because it is
meaningless noise.  If you've fallen off your plan so
you are storing new fat, you don't need a scale to confirm
that.  You already know when you've overeaten.

Just to let you know, my swing is 5-6 pounds so your 6-7
is not unusual.