Opened 3 years ago

Last modified 8 weeks ago

#3667 assigned enhancement


Reported by: John Borsi Owned by: Christof Gessner
Priority: minor Milestone:
Component: unit definitions Keywords:


I was a bit surprised when I was unable to find any unit corresponding to the 'Torr' in the UCUM specification. ( Yes, it's almost equivalent to mm[Hg], but they aren't actually the same. I do see the Torr occasionally used in clinical practice, so this would be a nice addition to the specification.

Change History (5)

comment:1 Changed 2 years ago by Gunther Schadow

Acknowledging this ticket. I am sorry that our ticket system is still defunct because of massive spammer attack. But someone noted this ticket via email.

You say:

"Yes, it's almost equivalent to mm[Hg], but they aren't actually the same."

In order for to act, we would need a proposal or at least some detail about how they are not the same, and specifically how, when "I do see the Torr occasionally used in clinical practice," how it is then anything else that mm[Hg]?

comment:2 Changed 2 years ago by Gunther Schadow

OK, Wikipedia

"The torr (symbol: Torr) is a unit of pressure based on an absolute scale, now defined as exactly 1/760 of a standard atmosphere. Thus one torr is exactly 101325/760 pascals (~133.3 Pa). Historically, one torr was intended to be the same as one "millimetre of mercury". However, subsequent redefinitions of the two units made them slightly different (by less than 0.000015%)."

Based on this definition we could add the Torr.

But I would caution that when clinicians use "Torr" they actually mean "mm Hg" as their amount of caring about this is proportional with their experience of measuring with actual mercury columns rather than Bourdon gauge. So in some way the addition of Torr as a slightly different unit is defeating a practical purpose.

Last edited 2 years ago by Gunther Schadow (previous) (diff)

comment:3 Changed 3 months ago by Simon Cox

Perhaps the practical purpose is having Torr named within UCUM so that it can be selected from a menu in an application that is configured using UCUM. If a user looks for Torr but can't find it they will get frustrated. The value of any quantity will be converted to (almost) the same Pa as it would if mm[Hg] had been selected instead, so no harm done?

comment:4 Changed 3 months ago by Brenée Mitchell

Owner: set to Christof Gessner
Status: newassigned

comment:5 Changed 8 weeks ago by Christof Gessner

I am in favor of adding a code for the torr. Also, review the definitions of the other pressure units, including Pa.

Some work to be done in finding a valid symbol that is free of conflicts.

Prefixes should be allowed.

What is the best reference for the definition? Maybe link it to the BIPM resolution related to the standard atmosphere?

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