An exciting triangulation feature has just been released at 23andme. It is only for profiles that have transitioned to the new site and have selected open sharing (for now). The feature shows you the relatives you have in common with one other profile and whether or not they triangulate with the two of you.
To use this tool you go to Tools > DNA relatives > People and pick a DNA relative to look at. At the top of the comparison page there is a menu item “Relatives.” Click on it to skip down the page where you will see a display like this (names removed for privacy):
When there is a “Yes” in the right hand column, there is a DNA segment in common between the two people you are comparing and this third person thus you triangulate. A “No” means that although you each share DNA with this relative, there is no segment of DNA where all three of you match. Click on the Yes (or a No) to see the three of you compared in the chromosome browser.
Once in the chromosome browser, you can use the “Update View – Edit” to add more people to the comparison with the first person. This is the same chromosome browser that you get to from Tools > DNA relatives > DNA
Jason Lee has done a nice write up with more details on his DNA blog at Tumblr:
Sadly you cannot use this tool with relatives still on the old site, since they have not yet been able to opt in to “Open Sharing” yet.