You have different decrease rates going on at each edge. The armhole edge decs a stitch every row for 5 rows, then every other row 3 times. While at the other edge you dec every other row for 2 dec rows (the next one and the 2nd one after) then it switches to every 4th row on that edge.
Dec one st at armhole edge in every row 5 times, then in every full atl row 3 times. AT SAME TIME dec one st at front edge in next row, then in every foll atl row 1 time, then in every foll 4th row until 24 sts rem.
sue- knitting heretic