Opened 7 years ago

Last modified 15 months ago

#169 wontfix enhancement

Add arbitrary unit for absorbance [A'U]

Reported by: John Snyder Owned by: Christof Gessner
Priority: minor Milestone:
Component: help Keywords:


Used in conjunction with optical density, has the absorbance unit [A'U] been considered for inclusion in UCUM.

Change History (7)

comment:1 Changed 7 years ago by Gunther Schadow

We need a literature reference for this.

comment:2 Changed 7 years ago by Christof Gessner

Collection of arguments and facts:

Absorbance is defined as the log of the transmittance. Transmittance is defined as the ratio of received and transmitted radiant flux. As such, Absorbance is a numerical value without a unit.

Some numerical scales that are conventionally used are assigned a unit symbol with the value "1", see for example Hounsfield unit "[hnsf'U]". However, such an assignment should only be made when an impact on patient safety is present.

Absorbance is not an arbitrary unit - another argument not to use something similar to "A U" here, as it might be misleading and be used with the meaning "arbitrary unit".


IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught? and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. doi:10.1351/goldbook.

Definition of the quantity absorbance, symbol A Logarithm of the ratio of incident to transmitted radiant power through a sample (excluding the effects on cell walls). Depending on the base of the logarithm a decadic and Napierian absorbance are used. Symbols (for the quantity): A, A_10, A_e. This quantity is sometimes called extinction, although the term extinction, better called attenuance, is reserved for the quantity which takes into account the effects of luminescence and scattering as well.

Last edited 7 years ago by Christof Gessner (previous) (diff)

comment:3 Changed 7 years ago by Christof Gessner

Owner: set to Christof Gessner

comment:4 Changed 7 years ago by Gunther Schadow

Status: newreject_proposed

I agree. So do you move to reject? This is done by toggling open the Modify Ticket section and click the radio button "propose_reject". Now I am doing that, and if you agree to this move we have it rejected.

As another comment on the subject matter, absorbance depends for the practical purposes that I know on the wavelength of light going in.

comment:5 Changed 7 years ago by Gunther Schadow

Dear GHSPACDC1, when you registered in the old version of the software, it allowed you to choose this all upper case user name. In the new version of the software I am unable to assign you to the group of verified users.

I have therefore changed your username to lower case "ghspacdc1" and verified this, but I don't know if that works. If you cannot log in with the all lower case user name, please create another user account with a user name including lower case letters, then open a ticket with the request to be verified.

comment:6 Changed 7 years ago by Christof Gessner

Status: reject_proposedwontfix

comment:7 Changed 15 months ago by Christof Gessner

Component: help

As this is closely related to the log-calculus for power attenuation and amplification, i. e. decibel and the like, I propose to deal with the ticket in that context. There are already some informal UCUM extensions for such "logarithmic units" that are in use in the RTMMS system, applicable to medical devices (cf. Paul Schluter). We should strive for a systematc approach here, and then derive a consistent nomenclature and formlism.

Suggestion: postpone...

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