Today i was selling some of my BTC to my friend and I we had a situation that I want some opinion on it . Now i sent him what worth of $100.20 ( at the time of transaction ) . But what he received was $99.70 ( at the time of received ) . Now my question is what value we should take here? The value at the moment i sent or the value at the moment he received ? I know that $0.50 is really nothing but me and my friend entered in to debate and I really wanted to know which value to use ! . because if a big delay happened and the price changed a lot with big a mount of money it gonna be a real problem .