The simmer ring swivels to the side. By doing that and placing it on the burner, you can simmer your supper like no other stove can do. By having only about 1/4 inch of burner showing you can have a "keep warm" situation (at least on the regular stoves which provide extraordinary wind protection). Trouble is that when you then want to extinquish the flame you have to remove the simmer ring, WAIT FOR IT TO COOL, swivel the top back and then replace it on the burner. I use the pot gripper to reach down to get the simmer ring but it is not a stable grip. Has anyone solved this little glitch in an otherwise perfect cooking tool?
Just FYI Trangia makes a winter burner attachment which fits under the burner and preheats it with alcohol. I have had to modify the preheater by removing 3/4 of the absorbent insulation on the preheater - I found the full preheating regime to heat the fuel to the boiling point which is not a good situation.