Right out of the Easton tuning guide:
Use the Bare Shaft Planing Test to correct Fishtailing. Shoot three fletched shafts at a distance of 15 to 20 yards (meters), then shoot two identically-aimed, unfletched shafts. If the unfletched shafts impact left (stiff) of the identically aimed, fletched shafts, as seen in Fig. 11 (for a righthanded archer), either decrease the spring tension on the cushion plunger, increase bow weight slightly (if your
bow weight is adjustable), or increase arrow point weight.
If the unfletched shafts impact right (weak) of the identically-aimed, fletched shafts, as seen in Fig. 11 (for a right-handed archer), increase the spring tension on the cushion plunger, decrease bow weight slightly (if your bow weight is adjustable), or decrease arrow point weight.