Items  -  M o t i o n B l e n d e r

This block is visible when you have MotionBlender selected in the Effects List (the green diamond).

Additive Blending: This is where you choose between Additive and Averaged blending.  The default is Additive, which means that each pose will add to the other.

Channels (toggle switches):  Choose which channels you want to be affected by MotionBlender.  By default, all channels are selected.