DMR FAQs on Math Skills
(Rounding, Precision, Significant Figures, pgs. 7-8 of DMR Manual))
Would we need to explain why we were not reporting to the correct number of Significant Figures, in a case where the data from the lab does not have the correct number of significant figures?
If lab reports less precision, who is responsible?
The permittee is ultimately responsible for their DMR and should discuss this with their laboratory.
The rounding method varies from standard methods. Why is this?
To accommodate the various computer programs that are currently in use by many facilities we have opted to use this method.
What if a less than and a greater than symbol appear in the same calculation?
Under these circumstances, the greater than symbol will be used in all cases except for a minimum Permit Requirement, where you would use a less than symbol.
Our permit limit for BOD and TSS has 4 significant figures, but you can only get 2 significant figures for BOD and TSS. Is 2 significant figures OK to report?
You can only report as many significant figures as the analytical precision allows, so in this case you could only report 2 significant figures.
If the number of significant figures in the permit limit is 2, can we analyze to three significant figures?
Yes, the permittee can analyze their samples to more significant figures than the permit limit states, but when reporting on the DMR, the Sample Measurement value must be in the same number of significant digits as the permit limit states.
If the phosphorus limit is 1.0 (2 significant figures) and our lab result is .067, do we enter .067?
Yes, .067 is 2 significant figures.
Would a result of < 5 be a breach of the significant figures if our limit is 15?
If the lab gave you < 5, we understand that the lab reported it that way. You cannot make up extra significant figures. But if the lab can report more significant figures, request that they do so.
Why is 0.7 not two significant figures?
This is because the 0 before the decimal point is not a significant figure. Please see the significant figures rules on page 7 of the DMR Manual.
If we have more precise data than the number of significant figures required, do we report to the more precise number?
No, you report to the number of significant figures that the permit limit specifies.
For Fecal Coliform, do we use the math/significant figures rules?
Yes, the math/significant figures rules apply to all parameters.
If a parameter on the permit is marked for monitoring only, should we report it to 2 significant figures?
In the number 123.00 why are the trailing zeroes significant?
The decimal point before the two zeroes makes them significant. Please see the significant figures rules on page 7 of the DMR Manual for more information.
For precision, if our permit limit is 10, do we follow 2 significant figures?
Yes. In this example, because of the trailing zero, we are unsure of whether this is 1 or 2 significant figures. On page 7, the manual states that:
"If the permit does not specify the number of significant digits, Sample Measurements shall be reported in two significant digits, except in the cases of effluent TSS or BOD where single digit effluents are achieved."