# announcements


02/19/2022, 5:27 AM
Just wanted to clarify a few things about general bucketing and `trackingCallback`: • What if weights are changed in the json file for an experiment? Can a user change buckets if they have been bucketed in a certain bucket, but then the weights change for an experiment? Can a user change buckets in any other circumstance? • Is
called every time the experiment is viewed or only the first time an experiment group assigned? I believe from my tests it is the former.


02/19/2022, 6:55 AM
Hi Jed. 1. Yes, a user can change buckets if you change weights. We do deterministic hashing based on the weights and the user id (or whatever the hashAttribute you're using). Since we don't store user states in any cookies, we have no way to knowing what variation the user got before. You can read about it here: - We have a few ways to handle this within GrowthBook: one, you can adjust the over all experiment exposure safely (ie, run a 50/50 A/B test against 10% of your traffic, then change that 10% to a different percentage). With GrowthBook, users who are exposed to both variations (for whatever reason) can be excluded from the results (and will be by default). 2. Yes, it's called every time.