PS/Internal Activity:- Work Centre to have unit of Measure other than time

PS/Internal Activity:- Work Centre to have unit of Measure other than time say EA.

I wish to use EA as UOM in WCentre of Internal Act. When I put EA I get this message:-

"Enter a time unit, since you have entered either work or actual workIn wormk"

Current settings are in WC:-

Basic Data Tab:-W.C. Categ:- 0006,

Cap Categ- 001, other form -SAP008 and 002, SAP 008,

Scheduling TAb:-WOrk Dimension - No dim., and Work Unit- EA

In Capacity detail also I ahve given 700 units = 9 hr of work

Standard av. Cap = 08.00.00 to 17.00.00

Thanks