Here is a video that may be helpful. Nock left for a left handed archer is too stiff. A .400 spine is equivalent to an 81-84# wood arrow shaft. Another variable is the bow cut to center or outside of center. A self bow not cut to center needs weaker while a metal handle recurve cut past center will need more spine. Bow weight is only one variable in quest for the proper best flying spine arrow shaft. String material, strands, length of arrow, weight the head, length of broadhead, etc. Hope this helps...