Strange Frame Rate Reports

Hi guys so im not really having issues but im actually having some confusion regarding FPS.

So when you run a game on the Engine “Built in” and even a external Engine and use FPS software the reading of FPS seems really odd for instance my game is built to run in 60 FPS and it does just that how ever the Built in and External Engines read something like 20FPS , 18FPS even dough no performance has been sacrificed at all.

Does OpenGL read FPS differently?

What program are you using to report framerates and what operating system are you using?

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Its just Windows 8.1 and Blenders Framerate and Profile the other FPS software i dont remember i have not used it in a long time since i uninstalled it.