I had written the following sentence in a manuscript:
After each transaction, the balance of the sender account equals their balance immediately before the transaction minus the amount of funds transferred
which a native English speaker reviewer corrected as such:
After each transaction, the balance of sender account, equals the balance immediately before the transaction minus the amount of funds transferred
(The definite article before sender account was removed, an additional comma was added before equals, and their balance became the balance)
For context: this part of the manuscript describes how a monetary transfer-like transaction in a system implies that, for instance, if a person A has a balance of 100 pounds and sends 10 pounds to B, then immediately after the transaction takes place, A’s balance must be 100-10=90.
I am not a native speaker, but to me, a definite article the is really missing in the altered version. I would understand the change if the word account was also removed and the sentence would say ‘After each transaction, the balance of sender equals…’ The proposed version sounds strange to me.
Secondly, I think changing their to the makes the sentence less clear. Does it not make sense in English to refer to one’s balance? If the is used, the statement is no longer explicit about the fact that it is the sender’s balance that changes as described (as obvious as it is, but that is beside the point).
Thirdly, I also do not feel like a comma is needed before equals, but I may be wrong, of course. I am not very good at commas.
Do you think the proposed changes are indeed better in the grammatical and stylistic sense? I am happy to accept that I am wrong, but I would like some explanations for these changes to learn. Thank you in advance.