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You can open the Add Custom Counter wizard by clicking Administration > Custom Administration> Custom Counters, and then clicking selecting Add in the Custom Counters view.
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Understand why the SQL Server counter grows
Many SQL Server counter values start at zero when a server starts and then grow persistently from there, including most of the values in the sysperfinfo system table.
For example, the Buffer Manager Page Lookups/Sec counter in the value collected mode always shows the total number of page lookups since the server was first started, while when in the value per second mode, it shows the number of lookups per second during the monitored period.