Why two transfers of the same SOL can show different fees
Two people can send the same amount of SOL and bring us printouts with different fee totals. The usual reason is a priority fee on one of them. The sender attached an extra amount so the leader producing the next slot would have a reason to include that transaction sooner while the network was busy.
The extra amount is tied to compute. On the receipt we look for a price per compute unit and for the compute-unit limit the transaction set. The priority fee is the meeting of those figures, not a second copy of the signature fee. The base 5,000 lamports per signature is still there underneath.
How the table shows it
On Saturday mornings the second sample in the folder is a transfer with a priority fee, and the first sample is the same shape of transfer without one. The group writes both totals, subtracts the signature line, and puts the remainder in the middle column. Then they find the compute-unit price on the page and say it aloud. The point of saying it aloud is modest: the middle column should have a source on the paper, not a shrug.
We do not tell the table what price to attach next time. Fee markets move, and a number that cleared quickly on a quiet Tuesday can be a poor guide on a crowded afternoon. The library’s job is to show where the extra lamports are printed and how they differ from the signature line.
A mistake we see often
People add the priority fee to the amount of SOL that was transferred and then describe the sum as the cost of the payment. The transferred SOL went to the recipient. The signature fee and the priority fee were the cost of having the transaction processed. Mixing those on one line makes a later receipt even harder to read, because the next one will not repeat the same priority.
If your own printout has a priority fee and you want it marked in the middle column beside a librarian, that is a window-desk sitting, not a Saturday. The table works only from shared samples, so nobody is reading a personal receipt across from a stranger.