This rotator will share out the hits based on the weight/ratio set for each URL, each weight can be a figure between 1 and 100, and the total of all weights cannot exceed 100.

Why do my weights change after they have been saved?
Because they total more than 100 and have to be adjusted.

Do my weights have to total 100?
No they dont, if you had 3 URL's in your rotator you could set their weights to 3,2,1 this means the first URL would get three times more traffic than the third URL and the second URL would get twice as much as the third URL. Setting the the weights of the URL's to 30,20,10 would share our the traffic the same way.

How even is the distribution of the hits?
The distribution of hits is based on the law of averages, this means each URL will get close to the correct number of hits but it will not be exact. To show you this distribution we sent 1000 hits to a rotator setup with their weights set to 3,2,1, ideally this should have resulted in the hits being distributed as follows 500/333/166, with the first URL getting 3 sixths of the traffic, the second getting 2 sixths and the third getting 1 sixth of the traffic, below is the real world results (We ran the same test 5 times) as you can see the results are fairly close to 500/333/166 but not exact.

504/325/171
491/343/166
515/336/149
491/348/161
513/334/153