What limits how large time compression can be?
 

SOmetimes, time compression is limited to 4, when my view is outside the sub, other times TC can go higher than 2048 when in map view. I don't recall the TC for outside views not able to go higher than 4! Inside the sub TC is limited to 32. Is this a MOD issue, or an Options variable?

Depends upon where you are. Close to land, you're limited to 4x. Other times on external, you'll be limited to 32x. Someone else will have more / better details on the other limitations. The max is 8192x, which while "convenient" at times, really stresses the game engine. I've had it not come out of 32x very politely before, and seen the explosion on my deck from a shore battery shell just as the game was getting it to 1x. "We're under attack!" no kidding... not cool. But such is life with time compression. Use as little as you can stand... 'Course, my butt gets sore sitting too long...

As you describe that's what I expected, but, I'm in middle of South China Sea not near any land but two pesky destroyers are looking for me within 1500 yards, I'm 180 feet deep but with external view my TC will not go beyond 4! But in map view the TC goes as high as I make it! Something has changed that I don't know what with TC and external view.

Have you got Silent Running on, or are you in shallow water? In the upper right corner... I was driving along doing CTD (Crash Test Dummy) work in a Single Mission I had been noodling with, and took my boat to 200, trying to get below a thermal before 3DD got close to me. Didn't happen. "We're taking ~damage~ SIR!" I'll sur you, you surly - say ankh? Water spraying every where... What thuh? Look at the damage screen, and I've got 50% hull damage (at least I didn't have to wonder if that meant what I'd lost, or what I had left). I had not gotten a 'verbal' warning, but there in the text box was "We're close to the bottom.", and in the upper right of the screen was that cute little icon for shallow water. Chart didn't show it, but there it is, big as a fleet boat hull... just about then, the cans started raining down on me. This being FotRS Ultimate, I was treated to the ~best~ IJN ASW available in game, and that's a side-thrower coupled with two hedge-hogs, doin' their best wagon wheel dance... "Around your partner, doe sea doe, drop yer ash cans, boom they go..."

In addition to what propbeanie wrote, your computer will limit how high of tc you can use. Outside of the game limitations (outside the boat, close to land, etc.), without other units around, I can get tc up all the way without problems. Others have said they can only get tc up to about 4000 before encountering lag issues. Once another unit is close, my computer starts to noticeably lag. I use the tc/stopwatch lag much to my advantage.

well, I just realized that those pesky DDs hit me causing 25% damage which probably qualifies for "critical damage" which then limits TC as stated in the Main.cfg file (I think that's the one).
Lesson learned:03::oops:

In Data\Cfg there is a cfg file that will adjust time, however be careful.

I didn't like that the game would only slow down to 8x or whatever when an aircraft was detected; even at 8x they are on you fast. Other settings also bothered me so, here's mine with some minor adjustments.

These need to be adjusted before a Career is first started and with an empty SH4 Saved Games folder in My Documents, because they move over to the \Data\cfg folder in the SH4 Saved Games folder in My Documents, or you can adjust that existing Main.cfg file in the My Documents Saved Games SH4 folder directly.

This is the section in Main.cfg.

[TIME COMPRESSION]
TimeStop=0
RealTime=1
LandProximity=32
CriticalDamage=1
CrewEfficiency=128
AirEnemyDetected=1
SoundEffects=2
CharacterAnim=4
EnemyDetected=1
RadioReport=1
Particles=8
PrayState=8
HunterState=32
3DRender=32
Maximum=8192

In the archives here at Subsim is a post with explanations for each setting that I copied and posted into my notes way back when, but the main settings are pretty much self explanatory. Below is that post from my notes:

Somebody (maybe Ducimus) wrote:
Happy Hunting!

On top of all of that, your machine's CPU and memory factor into whether or not you can use TC up to the maximum allowed in the configuration files. If the game CTDs, you pushed it too far.:D:D

Thank you Aanker, I always like learning more about the how's and what's of SH4 just as much as playing it. Perhaps you can tell me just what UPCLocalization.tsr does.
And, Roger that RR.

Yes, the mysterious UPCLocalization.tsr can be opened with a plain text editor like Notepad, NOT Word, and you can scroll through it. The information in it is called by other files to display in-game in many different places.

When you open it you can see the various entries and their locations. Rather than Notepad I use a program called NoteTab Pro. The NoteTab Light version is still free. http://www.notetab.com/
Some people prefer other programs for text & html editing.

Scrolling through it, when you get to the Ammunition section in Stock for example, you can see that it is pretty blah without useful descriptions. I like to think in Imperial measurements like feet & yards, US WWII Skippers used it.

Here is the entire Ammunition section in UPCLocalization.tsr from the Guerrilla Submarines Spyron Mod:
In-game you will recognize the ammunition info from the Tab when you are outfitting your boat to go out on patrol and other places.

I hope this helps a little.

Happy Hunting!