The display refresh for NT is0.5 sec default. What does the system does every 0.5 sec besides repainting all prior bars and indicators? If I set the refresh to 5 minutes in a 30 min chart, the current price will still move tic by tic or I will receive a picture every 5 minutes?
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As every tick comes in, NT needs to build the bars, pass the data around for the indicators/strategies to update their values, process orders, update DOM, etc. There is a lot of work to do other than updating the GUI, which can be a large task by itself depending what you have displayed. The NT architecture is mostly single threaded (the GUI is updated on a single thread), and the update interval is meant to reduce the workload on the CPU to make sure that the other critical tasks are processed in a timely manner.
Updating the display every tick is only an issue when lots of ticks are arriving in a very short interval. The display can only update so often in terms of how many updates you can see with the human eye. I think of it in terms of frame rate. So can you see 100 updates per sec? If we use 100 updates per sec, then the update time would be 10 ms (which is also getting down into the physical display refresh times).
So, if you can only see so many updates, then by limiting the number of updates, you free up the CPU to do the other tasks. On the flip side, when there is nothing else to do, I suspect that NT just updates the screen (i.e. the display delay is only injected when there is something to wait for). So, for your example of a 30 min chart, using a larger update interval really does not make any sense.
The update interval is there to primarily make sure that under heavy load the system remains responsive and gets the critical tasks done first, while still updating the screen in a timely manner.
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