But the document says:
To minimize overall fuel consumption during flight, a low cost index must be
used. As the climb phase is fuel consuming, it is advantageous to minimize climb
duration. This is achieved at the maximum rate of climb speed.
CI = 0 ⇒ IASECON = Maximum rate of climb speed
For Cost Index = 0, IAS Econ is maximum rate of climb.
For higher cost index the airspeed is increased up to VMO-10.