What's with these mass discrepancies?

[KocLobster]

I guess the answer just isn't obvious to me. Why do these two different masses differ? Why do they report different weights? The report on the bottom right is stock, of course. The report up across the top of the screen (and the tiny one on the bottom left) are thanks to KER. KER is awesome and my favorite, and I am leaning towards trusting it's numbers over the stock game's numbers. I linked it for anyone that's new or never tried it before.

Does anyone know why this discrepancy exists, and which one is the accurate one? I have started a second save with a pretty drastically different mod set; it contains KSPI-E, along with a number of other really cool and complex parts mods, and with a bit more difficulty to it (I guess this isn't very relevant). As such, and because it's still pretty early in this career, it is really important for me to know which one of these is correct. Even if the stock one is wrong, it doesn't seem to matter because that's what the game goes off of for determining if the launch pad can support the rocket (I just started this new career, it's still a un-upgraded launchpad).

KER says the mass is 7,740kg's, and the stock game recognizes the ship as being OVER 9000!!!! (kg's)

http://imgur.com/ocsAAdS

As always, thanks KSP community

Edited March 26, 2016 by KocLobster

[Rocket In My Pocket]

Well...if they are using U.S. tons, 7740 kg's is roughly 8.5?

[KocLobster]

It's nearly a 1:1 ratio though isn't it? 1 ton is roughly 900kg's. So there is still a discrepancy of about 400kg's, right? Stock thinks the craft weighs 400kgs more than it really does (or KER thinks the craft weighs 400kgs less than it really does).

Edited March 26, 2016 by KocLobster

[Rocket In My Pocket]

1 minute ago, KocLobster said:

It's nearly a 1:1 though isn't it? 1 ton is roughly 900kg's. So there is still a discrepancy of about 400kg's, right? Stock thinks the craft weighs 400kgs more than it really does (or KER thinks the craft weighs 400kgs less than it really does).

I agree, something is definitely going on here.

Maybe the pic is just fuzzy, but it kinda looks like the part count says 18 on the standard HUD. Could just be a blurry 3 though.

My only other idea is that one is counting the fuel while the other isn't?

[KocLobster]

15 minutes ago, Rocket In My Pocket said:

I agree, something is definitely going on here.

Maybe the pic is just fuzzy, but it kinda looks like the part count says 18 on the standard HUD. Could just be a blurry 3 though.

My only other idea is that one is counting the fuel while the other isn't?

That's actually a blurry 3, there are 13 parts.

I thought of that too, and checked it to be sure. I also tried changing the tank contents, and both of these things had no bearing on the stock's calculation of weight, which makes no sense. The weight should clearly change when you slide down the fuel contents and have a tank at less than 100% capacity, but stock KSP doesn't seem to realize this.

I've concluded stock KSP can't math.

Edited March 26, 2016 by KocLobster

[FancyMouse]

Is that a mod part or stock part? Only problem I know about stock part is fairing, but I don't see that in your picture. If it's mod part, you need to go to the mod thread to ask - it's their responsibility to report their mass to KSP.

[Crzyrndm]

1) The discrepancy exists because of how mods have to modify part masses currently. It has to be done in two places to match up the real weight and the engineers report. Post-1.1 this won't be a thing so hopefully the engineers report will match up properly
2) KSP uses the tonne/metric ton (1:1000kg) not that weird imperial unit

I would be significantly more suspicious of the engineers report as it requires an additional step that doesn't affect flight performance. IIRC IFS was having an issue with that a month or two ago

Edited March 26, 2016 by Crzyrndm

[KocLobster]

If the stock is wrong, why does stock not take into consideration when fuel tanks aren't completely full. Clearly the weight goes down if you don't have a full fuel tank..but it doesn't seem to know this. This has nothing to do with stock or nonstock parts.

[Rhomphaia]

1 hour ago, KocLobster said:

If the stock is wrong, why does stock not take into consideration when fuel tanks aren't completely full. Clearly the weight goes down if you don't have a full fuel tank..but it doesn't seem to know this. This has nothing to do with stock or nonstock parts.

For me, Stock engineers report does notice when I take fuel out of a tank. so maybe it does have something to do with non stock parts Or perhaps non stock fuels?

[KocLobster]

44 minutes ago, Rhomphaia said:

For me, Stock engineers report does notice when I take fuel out of a tank. so maybe it does have something to do with non stock parts Or perhaps non stock fuels?

I am talking about just a regular stock tank, and regular stock fuel. As in the picture above, stock does not recognize that the weight should be going down when I decrease the fuel.

[NathanKell]

@Crzyrndm in a way it will fix things. Because any mods that don't properly implement IPartMassModifier will have their changes destroyed on the next frame. So no more getting away with not implementing it.

[Crzyrndm]

@NathanKell Better than the current system where things are read from two different places (and the interface only affects the report/career limits. There's no obvious functional issues if you miss it). If you aren't told about how the engineers report works currently you won't know how to do it properly and you'll probably never know there's a problem until much later (how likely is it that a mod maker isn't using KER/MJ :P)

Edited March 27, 2016 by Crzyrndm

[Rocket In My Pocket]

12 hours ago, Crzyrndm said:

2) KSP uses the tonne/metric ton (1:1000kg) not that weird imperial unit

1 U.S. ton is 2000 lbs.

Is a 1:2000 ratio really that "weird" compared to 1:1000?

9 hours ago, KocLobster said:

I am talking about just a regular stock tank, and regular stock fuel. As in the picture above, stock does not recognize that the weight should be going down when I decrease the fuel.

That's really odd, I thought for sure stock KSP accounted for this, I'll have to check it out on my copy when I get a chance.

[ForScience6686]

Stock readout does account for partial or empty tanks.  I use this to calculate my dv numbers myself so I can confirm this.

[KocLobster]

@ForScience6686 Agreed, it does.

 

I think I figured out what the problem is, echoing what @Crzyrndm said a few posts above; the discrepancy exists because of the mods in some way.

I believe I'm seeing what the issue is now, it has something to do with Interstellar Fuel Switch. Changing the tank setup to something else (like LH2/OX, or Monopropellant, etc.) changes both the dry mass, and the overall mass of the tank because of the changes in weight as a result of the different contents (for example, LF is a lot heavier than LH2). KER has no problem realizing this and correctly displaying the new mass, but the stock game doesn't recognize this. It seems it is only able to perceive the original (stock) tank setup (LF/O). Just to note, it does not seem to matter if it is a stock tank or a Fuel Tanks Plus tank, or another mod's or parts pack fuel tank. So I guess this is probably something that I should post in the IFS thread.

Only very early in the game, before you have an upgraded launchpad/runway does this make much of a difference. However, my biggest concern is that the game calculates your mass on the stock's understanding of what the mass is, not the correct mass reported by KER. What if dV is also calculated in this inaccurate way too?

[ForScience6686]

I would guess the discrepancy is causing other issues as well with the mass being off.  But I would assume this would not affect much except for large high fuel ships.  Ker might give you the proper dv, but the game recognizes more mass so dv would suffer.

[KocLobster]

This is what I was afraid of...

[ForScience6686]

This is exactly why I run the numbers myself, and run vanilla.  The mods look nice, but had you missed this you may not have found out until a mission critical point.

[Crzyrndm]

10 hours ago, Rocket In My Pocket said:

1 U.S. ton is 2000 lbs.

Is a 1:2000 ratio really that "weird" compared to 1:1000?

Tongue in cheek poke at Imperial units as a whole

3 hours ago, ForScience6686 said:

I would guess the discrepancy is causing other issues as well with the mass being off.  But I would assume this would not affect much except for large high fuel ships.  Ker might give you the proper dv, but the game recognizes more mass so dv would suffer.

Except the *flight scene* uses the same mass as KER does its simulation on. Only the engineers report/career limits use a different number. If KER was giving incorrect numbers, the mod author would hear about it rather quickly >.>

Edited March 27, 2016 by Crzyrndm

[Renegrade]

On 2016-03-27 at 7:56 AM, Rocket In My Pocket said:

1 U.S. ton is 2000 lbs.

Is a 1:2000 ratio really that "weird" compared to 1:1000?

That's really odd, I thought for sure stock KSP accounted for this, I'll have to check it out on my copy when I get a chance.

Yes, it is weird, as it's actually 20 hundredweight (cwt -- well, US cwt.  British cwt is 112 pounds, which is 8 stone), which is 100 modern Avoirdupois pounds.   So it's really more like 20:100, not 2000 directly.  Which in turn is 32,000 ounces... or 512,000 drams, or fourteen million grains.   So 20:100:16:16:27.34375 (or 27 and 11/32 if you prefer for that last number) ... yeaaah... not weird at all.  Nosiree.  Totally sensible system.  Was NOT created by drawing numbers from a hat while drunk.  Honest!

That's leaving aside all the classical, pre-metric measurements for 'pounds', like Troy pounds, London pounds, and Merchant pounds, all of which have significant differences.  And forgetting to mention that a US ton uses the (modern, metrified) Avoirdupois system, and is actually defined as being '907.18474 kg'.  1:907.18474!  Excellent!

I'm so glad Canada switched to metric/SI when I was a kid.  That imperial junk used to give me the WORST headache.  10:10:10:10... is a lot easier to remember than 20:100:16:16:some-number-that's-almost-thirty-I-think(and also a different set of numbers from length measurements - 1760:3:12:6:12 -- leaving aside links and furlongs and blahblahblah). Plus it's a lot easier to skip units.  How many ounces is 16.5 tons?   16.5t is 16,500,000 grams.  Also.. can you be sure we're talking about short US tons, and not long British tons?  Or not some historical measurement of ton that is wildly different than a US short ton?  For example, old sailing ships used to be taxed based on a 'ton' that was actually an estimate of volume.  A very POOR estimate of volume to be specific.

PS.  I won't mention the quarter if you don't!  er, oops, dammit, I just did... Nobody saw that!  Nothing to see here, move along, move along! 

[Rocket In My Pocket]

18 minutes ago, Renegrade said:

-snip-

You seem to have strong feelings on this matter, I suggest a hobby. Maybe stamp collecting?

Imperial worked well enough to get the United States to the moon and back.

That said, let's not derail this thread any further into an argument about metric vs imperial.

[Renegrade]

7 minutes ago, Rocket In My Pocket said:

Imperial worked well enough to get the United States to the moon and back.

That said, let's not derail this thread any further into an argument about metric vs imperial.

Well, except that was von Braun's rocket, designed in metric, and only converted to imperial units for manufacture.  He really hated those feet and picas and drams and such.

I do agree that we're likely derailing at this point and I'm willing to agree-to-disagree here.

[Plusck]

3 hours ago, Renegrade said:

I'm so glad Canada switched to metric/SI when I was a kid.  That imperial junk used to give me the WORST headache.  10:10:10:10... is a lot easier to remember than 20:100:16:16:some-number-that's-almost-thirty-I-think(and also a different set of numbers from length measurements - 1760:3:12:6:12 -- leaving aside links and furlongs and blahblahblah). Plus it's a lot easier to skip units...

On the negative side, I live in a long-metric country (they basically started it, then tried to do the same to hours, days, weeks and months but gave up) and have seen one very bad effect of metric: kids can't multiply by twelve off-the-cuff because they have no historical reason to teach things like the 12 times table. It just doesn't appear on the curriculum.

This is beside the point for the thread, but it seems that the answer to the main question has been duly answered: certain mods are not correctly indicating the mass of their parts for the game to take it into account. Somebody should upvote the best and clearest answer for that.