Counter showing accumulated value

There are some performance monitors in a router in my network that shows a constant value (say 393219.0 for example). After reading documentation and looking at opmanager database, I found that these are counters never cleared, and the nms should show the incremented value between consecutive polls. How can I tell opmanager to show incremental rather than accumulated values?
The monitors are the standard "Big Buffer Hits", "Big Buffer Misses", "Buffer Create Failures", "Buffer Failures", etc.

Thanks