What does -1 mean when returned from custom WMI

Heres the data returned.

"Microsoft (R) Windows Script Host Version 5.6
Copyright (C) Microsoft Corporation 1996-2001. All rights reserved.

PageReadsPersec 15852354"

Using...

<CATEGORY ID="Memory Statistics" command="W2K3_Memory_stats.vbs" parseAll="true" ignoreLines="2" description="Monitors Windows 2003 memory Statistics">
<ENTITY ID="Memory Statistics" applyThresholdOver="Counter Value" threshold="Th6" storeValue="Counter

Value" storeHistory="true" units=" " comparePreValue="false" >
<PARSE token="1" name="Counter name" isEntityName="true"/>
<PARSE token="2" name="Counter Value"/>
</ENTITY>
</CATEGORY>

Thanks
Gary