If WGT were to abandon entirely the browser based game, and using Flash, and provide the game as a downloadable game written in C/C++, or even assembler, they could not guarantee a perfectly smooth swing meter on anything less than a real-time system. Windows, Linux, Mac, you name it, what you're playing on is not a real-time system.
Applications get to run only ever so often, and they get a limited amount of time. I'm speaking of desktop/laptop systems that are preemptive. On older systems you would be saddled with the blue screen of death.
Let's say that you need to lay down one pixel every two milliseconds in order to get a perfectly smooth meter. You don't get to use the CPU every two milliseconds. Not even if you're the only process running. You're lucky to get to run at 10-16 times that rate.
One thing you can do is use a timer event. Instead of using your whole time slice, you can give it up after you've done something and ask the system to come back to you in a smaller period of time, say 10 milliseconds. You will generally get that, depending upon the competition for the resources.
You can ask for an even shorter period of time, but you won't get it without changing the system's operating parameters.
If you use something like TimeBeginPeriod/TimeEndPeriod you may increase your precision from 10 milliseconds down to one. This is a potentially dangerous and harmful mechanism, so you need to invoke in it a rather tight period of time around your critical area. You won't get below one, in any event, on Windows.