Units Clarification

[gmanikta]

I have been refrring to the "Unified Code for Units of Measure (UCUM)" document for Units of Measure to standarize soem of the units used at our University of Iowa Hygienic Laboratory forthe various Environmental scetions.

I would appreciate if you can please clarify as to how teh following will be used per UCUM recommendations:

1. % by area...Will "area" be in curly or square brackets?

2. % by dry wt...Will "dry wt" be in curly or square brackets?

3. % by rec'd wt...Will "recd wt" be in curly or square brackets?

4. % saturation... Will "saturation" be in curly or square brackets?

5. There are some units used in Radiochemistry like "dpm" which stand for "disintegration per minute BUT they are real units by themselves...How shall we designate them using the UCUM rules?

6. Some more units like MGD (Million gallons per day), MPN (Most Probable Number), GPD (Gallons per day), NTU (Nephelometric Turbidity Unit)...How shall we designate them using UCUM rules?

7. Some units like "feet or foot" havebeen represented by "ft" since time immemorial. This hasbeen helpful for clients too to understand the unit. As per UCUM, we can use "ft" as either "ft_i" OR "ft_us", OR "ft_br". Isit possible to add "ft" to the description?

Your input would be much appreciated and will be very helpful.

Thanks, Gunjan

[gschadow]

Replying to gmanikta:

I would appreciate if you can please clarify as to how teh following will be used per UCUM recommendations: 1. % by area...Will "area" be in curly or square brackets?

You can put anything in curly braces, it has no influence on the meaning. According to the IUPAC Silver Book, % is 0.1 exactly and a % is a % regardless of what the dimension of the quantities are being compared in the ratio or fraction. So this same answer holds for the others:

2. % by dry wt...Will "dry wt" be in curly or square brackets? 3. % by rec'd wt...Will "recd wt" be in curly or square brackets? 4. % saturation... Will "saturation" be in curly or square brackets?

If you need to make a difference between those, you need to have a clear indication (code) in the your data that specifies the kind of property that is being measured. Area fraction, mass fraction, etc. These distinctions are not to be sought or found in the unit.

The distinction between received and dried is talking about mass as determined in different objects (before and after some treatment). Again, this distinction is never to be sought, expected, or even placed into units.

5. There are some units used in Radiochemistry like "dpm" which stand for "disintegration per minute BUT they are real units by themselves...How shall we designate them using the UCUM rules?

Like any other event, you can determine the frequency of these disintegration events.

You can measure the frequency of heart beats, breath excursions, disintegrations, reintegrations, hand clappings, foot tappings, and wolf howling per night, in all those cases, you measure the frequency of some event. The unit is 1/s (= 1 Hz), 1/min, 1/h, 1/(6.h), etc. You should never expect the description of the event in the unit. Specify the event that you are measuring in the code for the measured property and you won't need a specially looking unit.

6. Some more units like MGD (Million gallons per day),

isn't that easily done as 10^{6.[gal_us]/d?}

MPN (Most Probable Number),

that isn't a unit at all!

GPD (Gallons per day),

[gal_us]/d

NTU (Nephelometric Turbidity Unit)...

this one is the only unit so far that seems of any interest and potential for being added to UCUM. How is that NTU defined?

7. Some units like "feet or foot" have been represented by "ft" since time immemorial. This hasbeen helpful for clients too to understand the unit. As per UCUM, we can use "ft" as either "ft_i" OR "ft_us", OR "ft_br".

Actually, it is "[ft_i]" OR "[ft_us]", OR "[ft_br]".

Is it possible to add "ft" to the description?

The description says "foot" that is probably sufficient. And no, we can not just take one of these foot lengths and designate without a subscript, because they are different.

kind regards, -Gunther