For Excel 2003, =IF(ISNA(VLOOKUP([@Date],'H:\Haydn\[Mandy_Mill_Uptime.xls]Mandy_Mill_Uptime'!$A$1:$G$65536,4,FALSE)),0,=VLOOKUP([@Date],'H:\Haydn\[Mandy_Mill_Uptime.xls]Mandy_Mill_Uptime'!$A$1:$G$65536,4,FALSE))
For 2007 and up, =IFERROR(=VLOOKUP([@Date],'H:\Haydn\[Mandy_Mill_Uptime.xls]Mandy_Mill_Uptime'!$A$1:$G$65536,4,FALSE),0)