Following in the Nostr is just an event containing a list of pubkeys. So when someone follows you or you follow someone, you just put their pubkey into the list and publish it to relays, using this your clients can fetch this event to study the pubkeys you want to see posts from. So, your following list is a clear central point to find your followings and completely controlled by you. Now, how about followers? It depends on your definition of a follower. If you consider anybody checking your new post a follower, you won't find it never ever. Beacuse I can just search your pubkey and check your posts daily without clicking that button. But if you want to check how many pubkeys (users) have added your pubkey to their following list, you need to find all following list events on Nostr that contains your key. Since we can't connect to every relay running out there or be up to date always, the events we find with this conditions heavily depends on when we connect to which relays! So many clients may show you different numbers because: 1. They may connect to some specific relays for this that may miss some people who follow you. 2. They may filter out some pubkeys as spam locally or on servers (like primal) and don't consider their follow lists even if your pubkey is there. Or maybe just count any lists with your key they found on any relay which should show the highest number. But what is the best you can do if you are curious to find the number of people who have your pubkey on their list and they are non spam people with a chance of really seeing your posts, you can check npub.world by @Vertex and @Pip the WoT guy. For example:

- npub.world

This service is actively indexing roughly the whole relays out there and filter out spam relays with a Global PageRank Web of Trust algorithm and calculates a final number. Still it misses EXACT number of people see your posts, because: I can follow you but ignore you, I can don't follow you but check your daily. But this service is the most accurate way to check real pubkeys following you with the meaning of having you in their follow list event.