metric mastery rule clarification

[R S]

Hi,

I know it's a bit late in the game, but still asking for clarification:

The rule states:

Measurements must be made using the supervisor-supplied instruments, expressed to the instrument’s resolution (the smallest division/markings/graduations on its scale) plus one estimated digit (if appropriate/analog).

To receive points, measurements must be expressed using the proper resolution and estimated digit appropriate for the instrument(s) provided, and the proper unit of measurement.

The question is:

Let's say I've a ruler with dm, cm and mm markings on it. They ask you for the answer in dm. Let's say the ruler shows somewhere between 3 and 3.5 dm. How many significant digits should we put?

Do we put 4 sigfigs something like: 3.421 (because 2 represents mm marking on the ruler and 1 is the estimated digit)

Or do we put 3 sigfigs something like: 3.42 (4 represents cm and mm is the estimated digit)

Or do we put 2 sigfigs something like: 3.4 (4 cm is the estimated digit and that's it)

Any help in this regards, is greatly appreciated.