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# Fuel expenditure

## Question

My plane was doing 0.13 fuel units per second, so i figured i'd time how long it takes to expend a unit of fuel, it took 23.56 seconds.
But my calculations predicted far different from that result. My calculations are bellow.

0.13 units/s
1/.13 = 7.6923076923076923076923076923077 (seconds delay between each unit use)

As you can see i predicted ~7.69 seconds, but i expirienced 23.56 seconds. A ~206.37% increase.

I've added a screen-shot i took around the time of calculations in-case it helps.

Can anyone tell me where i went wrong in calculations or if something like my frame rate is causing odd updates or something?
(I had on average 11 FPS, and i timed the fuel expenditure with a stopwatch with 1/100 second accuracy.
Also note that in the screen shot it has .09 but at the time of calculation it had .13)

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@Sarahleth From what I can tell from your screenshot your mission clock is showing yellow digits instead of green digits. This means that the game is slowing playback somewhat in order to have more CPU cycles to compute physics. In atmosphere flight and/or high part counts will often have this effect. If the clock is red then it means that the game is running seriously slow in order to compute all of the calculations the game needs to do in order to run complex physics on high part count scenes.

It should be easy to test if this is the cause of the discrepancy. The mission clock is counting time elapsed in the game world, not real-world time, and runs more slowly when yellow/red. All you have to do is see if the in-game mission clock is keeping up with your stopwatch.

Edited by HvP

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I can't say for sure, but more than likely its a frame rate thing.

I'm not 100% sure about how KSP does physics, but I think its like per frame. Soif you have a slower frame rate, it might cause the game time to physically run slower.

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1 hour ago, qzgy said:

I can't say for sure, but more than likely its a frame rate thing.

I'm not 100% sure about how KSP does physics, but I think its like per frame. Soif you have a slower frame rate, it might cause the game time to physically run slower.

That's what i was thinking. But it'd be a bit crap if the stats that they show are only accurate at 60 FPS or something similar.

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7 minutes ago, Sarahleth said:

That's what i was thinking. But it'd be a bit crap if the stats that they show are only accurate at 60 FPS or something similar.

True.... Maybe a simple way to check if a game second is equivalent to a real second is to level out the plane and let it fly for 30 seconds or something. Using the speed output, calculate how much distance SHOULD have gone by and compare how much distance has actually gone by.

Edited by qzgy

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6 minutes ago, qzgy said:

True.... Maybe a simple way to check if a game second is equivalent to a real second is to level out the plane and let it fly for 30 seconds or something. Using the speed output, calculate how much distance SHOULD have gone by and compare how much distance has actually gone by.

Good idea. It would be quite simple yeah.

Example:

Just level the plane and go at for instance 60 m/s travel for 30 seconds and i should go 1800 metres.

But if for instance i go 1000 metres i know time is weird. So i work out the difference: 1-((1800 - 1000) / 1800) So i now know that 1 second real life is 0.55555555555555555555555555555556 seconds in game.

(Though that was just an example of calculation and i'd need to test it later to get actual results)

I'll have ago at giving the game a test at some point as it would be interesting for many applications.

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1 minute ago, HvP said:

@Sarahleth From what I can tell from your screenshot your mission clock is showing yellow digits instead of green digits. This means that the game is slowing playback somewhat in order to have more CPU cycles to compute physics. In atmosphere flight and/or high part counts will often have this effect. If the clock is red then it means that the game is running seriously slow in order to compute all of the calculations the game needs to do in order to run complex physics on high part count scenes.

It should be easy to test if this is the cause of the discrepancy. The mission clock runs more slowly when yellow/red. All you have to do is see if the in-game mission clock is keeping up with your stopwatch.

Oh yeah i forgot about the clock, and thanks i never knew about the showing of yellow/ red to indicate the game's slowing down. Thanks for the help.

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