The concept of Ethereum's PoS originally started in 2018 and a lot of work has been done through years to produce the first draft of the CL's specification. The beacon state is the main data structure that represents the beacon chain's status at every moment. For the beacon chain, time is decomposed into slots of 12 seconds and epochs of 32 slots. Each beacon node stores the beacon state with a specific slot frequency; for instance, one can store a beacon state every 2048 slots.

Any state of the blockchain can be restored by going to the nearest beacon status previous to that moment, and then apply the blocks on top until we reach the desired slot. We used this data structure to produce the data shown in the dashboard as it has all the needed information about the validators tasks and the blockchain status in the given epoch (such as attestations, balances, and missed blocks, among others). This ultimately enables us to calculate the maximum reward a validator could obtain theoretically at each epoch, as well as the actual reward obtained at that epoch.

Side note: all the details and explanations presented in the following sections reference Ethereum CL's rewards specifications for the Altair/Bellatrix hard forks (as Bellatrix inherits most from Altair's specifications). This is because these are the specifications relevant near the Merge.