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adding description of options for sig figures, and suggestions to minimize student frustration. Minor wording/structural changes.

\label{Significant_Figures}
A \textbf{significant figures} specification is an optional setting that 
tells LON-CAPA how many significant
figures there are required for the answer, as either a single number, e.g. 3, or a range of
acceptable values, expressed as \textbf{min,max}. The significant figures field can be omitted if you do 
not want to constrain the number of significant digits in the student answers.

The system will check to
ensure that the student's answer contains the required significant digits,
useful in many scientific calculations. For example, if the computer answer is {}``1.3'',
and the problem requests three significant digits, specified by (entered without quotes) 
{}``3'',  the system will require the students to type {}``1.30'',
even though numerically, {}``1.3'' and {}``1.30'' are the same. A significant
figure specification of (entered without quotes) {}``3,4'' means both {}``1.30'' and {}``1.300''
are acceptable. 

Authors should be clear in the problem statements to tell students the required
number or range of significant figures. If the student response does not contain 
the correct number of significant digits, the LON-CAPA response will 
tell students to increase or decrease the digits in their response, but it will not
tell them how many digits to use. These responses do not use up
the number of trials, but such responses are frustrating for students. If you would like to ensure
that at least three significant digits are used, then a specification such as 3,15
ensures at least three digits are used, but will quietly accept up to 15.

Note that care must be used when using formatted computer answers together with 
a significant digit specification.
You must ensure that the formatted answer provides enough significant digits.
To test the formatted answer, LON-CAPA converts the computer answer,
as generated in the script block, according to the
format attribute in the numericalresponse tag, e.g. 3f.
Then LON-CAPA separately applies that number of significant
figures to the computer answer, and if that result
falls outside the range specified in the significant digit parameter, 
it "grades" the computer answer as SIG\_FAIL (i.e., not correct). 
It is a good idea to use the problem testing environment to test plenty of different
randomizations to make sure that your format and sig digits parameters are compatible.
This helps ensure that the formatted answer has enough significant digits.