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X-Plane Simulation Rate Enforcement - Insider and outsider.

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Thank you for the link to XSquawkbox Knowledge base.


20FPS means 50ms (50ms*20 = 1s)


If, during the elapsed 1s, FPS is down to 10FPS one time, there will be 100ms with a low frame rate and 900ms with a normal rate. So a short freeze. If it happens rarely it is OK.The FPS average is <20FPS, strictly.


if, during several consecutive seconds(2,3,10,30) , FPS drop under 20FPS, then during the elapsed time (2,3, 10, 30 s) the average speed will be < 20FPS. And for sure the real position of the aircraft will differ from the one it should be.

The plane is slower than indicated. It is critical if you are not alone in the area.


By the way, FPS are variable as the input in Windows scheduler are variable too.

So you may observe on the same 1s duration, FPS under 20 and also, some or a lot, FPS upper 25 or 30, or 40. So the lone way to check is to compute dynamic average speed on a period, and check if average goes under 20 as that means that the plane is slower than it should be on that period. If you have FPS drops under 20 and FPS greater than 30, the average will possibly be > 20 and the impact in delay or position is 2 digits after the comma !


It is also important to measure the %age of FPS counted under 20FPS on all FPS count, as it allows to compute the whole delay : time and distance, during the whole flight.


But it is necessary to be smart too with this %age

For example if 25% of whole FPS has been under 20FPS your plane will be late and will be slower than indicated for controller or other pilots.


If the %age of FPS under 20FPS is under 1/1000, or less, during your flight, it is hidden, and mixed in all approximation already done in other computation.


The Check_FPS.lua(*) script uses computer's clock to count X-plane FPS variation. X-Plane gives its own vision of what are FPS, the script follows variation and memorize them and count the lasting low FPS period, the measure is instant FPS and average FPS, the check is scheduled by Windows as the lua engine is requesting Windows clock.


The new version of script allows to increment or decrement, by 5s step, the length of observed time, by default 31 s, it may vary between 1 and 61 s.


So using this script, one has two tools, one inside network client, one outside, to double check how the frame rate is evolving.



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