ACK seq number and number of retransmission

http://www.filedropper.com/up2

in the above TCP stream, I notice that the expected next seq number of no.9 TCP packet is is 1902. But the following ack number of the ACK packet is 1903, which is 1 more than 1902. I'm wondering whether it is due to the retransmission (NO.9 is a retramsmission of NO.8)? if so, then if there are N retransmission, the ack number is seq+N? if not, what are the causes for the inconsistency?