Trying to find a website

I remember a while back (I'm guessing 6 months to a year) I saw a website that was used for tracking weight loss, but built in showed the possible fluctuations of weight day to day.

So let's say I was tracking my weight loss and I am 190 one day and the next day I weigh in I am 194, when I put that in the website would tell me if I was within the normal safe ranges of weight fluctuation to remain losing weight.

I can't seem to find it, and thought it would be a great tool for my wife who is getting frustrated at the fluctuation of numbers on the scale.