ECON. If you manipulate the Cost Index, it will alter the ECON speed to a new scale, but it will still show ECON. We select 0 during climb, and usually 90 or leave at 0 is required. When you select 90, it shifts the speed up slightly in ECON. You can select 400 as max. It will still display ECON, but cruise speed will go up to M.865 or so. Any time you like, you can select a Manual speed in the FMS which will show as Mod Spd M.85 cruise and maintain that speed in VNav.