how to modify the fomular to look up two sheets?

[Dandan Zhu]

=IF(A7="","",-IF(HLOOKUP($A7,Calculation!$C$1:$HJ$801,801,FALSE)=1,0,J7*R7*I7*Q7/O7/100))

It looks up Calculation sheet at the moment, I want to look up both Calculation sheet and Calculation sheet 2.

Many thanks