Talk:Millimetre of mercury

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Intro

I spotted this in the intro section. It's obviously someone's notes, which belongs here (if anywhere) - definitely not in the main text:

new:in medicine measuring the pressure of CSF in supine position is about 65-200mmWATER(10-15mmHg)....while in sitting position there is add of +200mmWater in it ..value will be 265-400mmWater(20-30mmHg).

Add relation between mmwater&mmHg!! — Preceding unsigned comment added by 217.13.251.134 (talk) 10:06, 1 July 2015 (UTC)[reply]

History and definition

In this section of the article, if someone could provide an equation in scientific notation for the density of mercury, I think that would go far in improving the article. Erzahler (talk) 21:31, 2 October 2013 (UTC)[reply]

I'm pretty sure that the reference to speed of gravity is incorrect. Later in the paragraph there is a reference to acceleration of gravity and standard gravity, I'm assuming the author was meaning acceleration due to gravity throughout. Wikiangelo (talk) 19:14, 3 December 2013 (UTC)[reply]

Yes, I came to the same conclusion. The speed of gravity is a universal physical constant (in GR it should be equal to c, and it is the speed at which disturbances in the gravitational field propagate). The acceleration due to gravity on the earth is a much more parochial thing, and it does indeed vary with position on the earth's surface. I'll change it over. Archon 2488 (talk) 14:50, 20 February 2014 (UTC)[reply]

Exact definitions

This page says mmHg has 2 different exact values. How can this be? 188.114.164.7 (talk) 13:10, 4 May 2024 (UTC)[reply]

It's not a standard unit, so anyone can define it as (exactly) anything they want. To make the definition plausible it just needs to be (approximately) equal to the pressure exerted by a one millimetre head of mercury. If you want a precise unit, use the pascal. Dondervogel 2 (talk) 17:05, 4 May 2024 (UTC)[reply]

Adding to what Dondervogel 2 says: the EU published a value rounded to 6 significant figures, BSI and others the full definition as 13.5951 x 9.80665 Pa. Such variations and much greater ones are common outside the International System of Units - see calorie, BTU, survey foot or SCFM. NebY (talk) 17:12, 4 May 2024 (UTC)[reply]