Hello everyone, this is my first post on the forums!

I've currently designing a Game Engine in C#, using OpenTK. Note that; I'm ditching the 'GameWindow' methods, like load, update and render, and creating my own.

Because of this, I need to create a way to manage time in my engine (FPS, frames, delta etc). So far I've created a class, which can sort of handle time correctly.

Currently, if I run a game at 60fps, everything works fine. However, if I run it at 120fps, I only get around 111fps; (Note: I'm not rendering anything to the screen). Another funny thing is that I can set the fps to even higher, say 300fps and I get around 250.

I'm not sure why this is happening, maybe it's the inaccuracy of the Stopwatch class. Here is the update method of my game time class:

        public void Update(float max_updates_per_second)
        {
            /*
             * watch: a System.Diagnostics.Stopwatch object
             * CanProcess: Tells the game engine whether we're allowed to update and render then next frame
             * wait_ticks = The amount of milliseconds needed to wait until we can render the next frame
             */

            float wait_ticks = SECOND / max_updates_per_second;

            delta = watch.ElapsedMilliseconds - (float)lastTimeUpdatedFrames;

            if (watch.ElapsedMilliseconds >= lastTimeUpdatedFrames + wait_ticks)
            {
                frames++;
                canProcess = true;
                lastTimeUpdatedFrames = watch.ElapsedMilliseconds;
            }
            else
            {
                canProcess = false;
            }

            if (watch.ElapsedMilliseconds >= lastTimeUpdatedFPS + SECOND)
            {
                fps = frames;
                frames = 0;
                lastTimeUpdatedFPS = watch.ElapsedMilliseconds;
            }
        }

Any help on why my game time isn't accurate would be great!