The offset is the number of elements to 'move over' from the front of the array, or the index of the array to start from (however you want to look at it). The length is the number of elements that you want to operate on from that point.

Ie offset=2 and length=4 would operate on elements 3 through 6 the array. (element number 1 is offset or index 0)

/\/\averick
perl -l -e "eval pack('h*','072796e6470272f2c5f2c5166756279636b672');"