CT test procedures

The only thing we can PROVE with these tests is that INstability exists in the snowpack. If we perform the tests, and we find instability, then we know it exists. If we find no instability, then we only KNOW that it doesn't exist in the snow we tested. We have not ruled out the possibility of INstability existing in any other snow. Essentially, and INstability test that does not find INstability is a failed test.  

Everything Otter wrote helps clarify the subject. I think his entire post should be included in any discussion about stability test's and methods. Thanks for posting.

I found a link I thought I would share on the Extended Column test: www.fsavalanche.org/NAC/techPages/articl...6_ISSW_Simenhois.pdf

Thanks Otter, it has been a while since I was in a class. It still makes me wonder about the reason for a shear test though, or about it's inclusion as a test along side the others. It always seems like you get the information about the existence of a bad layer just by digging the pit. Then, on a day where the shear goes quite easily and a block slides just from the shovel being set behind it do you ignore that evidence because the compression test gave more reasonable results? And even though it is said to only identify a weak layer, intuitively it seems like it could be testing some of the same things as a rutchblock test but on a small scale because it severs the blocks connection to the snow upslope from it and lets it slide down on the bad layer like an airhockey puck, whereas a ct test seems to squish the air out the layers and maybe help the bonding on the small column that was dug.

Then, on a day where the shear goes quite easily and a block slides just from the shovel being set behind it do you ignore that evidence because the compression test gave more reasonable results? And even though it is said to only identify a weak layer [...].

No. I would not ignore the shear quality I observe while digging. It is valuable information, it's just not coming from a standardized test. All these quantitative tests (CT, RB, etc.) are appealing to us because we like numbers and have a sense that we can draw hard conclusions from them. However, your subjective observations during qualitative tests and non-standardized tests are just as, if not more, important.
Ultimately, it is a combination of all your observations that will provide the most complete picture of stability. Don't get sucked into focusing on one piece of information, especially if that piece of information seems to indicate STABILITY. It takes a lot of evidence of STABILITY to give me confidence, but only one sign of INSTABILITY to make me concerned and behave more cautiously.

You can run a lot of yellow lights and even a bunch of red lights and get away with it, but eventually you will suffer a consequence, be it just getting pulled over and given a ticket or a warning, or a severe crash that can result in injury or death. In the end, what did running all those lights really get you?
You can also ski a lot of slopes in unstable conditions and get away with it, but you never really know when you will get caught or what the consequence will be. So be conservative.