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H.j. Woltring, Fax/tel +31.40.413 744
06-12-1992, 09:43 AM
Dear Biomch-L readers,

On the C+HEALTH list, the following item with some implications for
Biomch-L was received this evening. Any comments from our list?

Regards -- hjw.

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Received: Fri, 12 Jun 92 22:27 MET
Date: Fri, 12 Jun 1992 16:09:26 EDT
From: Chris.Grant@UM.CC.UMICH.EDU
Subject: Monitor height
Sender: Health effects of computer use

> Ed Wilds says: Height does matter. When you sit at your computer
> station you want to maintain good posture. Tilting the head down
> to look at a monitor that is low is not good posture.

This has potential for being an interesting conversation! The
ANSI/HFS VDT standard says the top of the monitor should be anywhere
in the range between eye level and 60 degrees below eye level ... an
extremely wide range. This is one reason why I said "height doesn't
really matter." Perhaps my sweeping statement was incorrect, but
I still say that it's easy to put the monitor too high, and hard to
put it too low.

The Canadian national standard says from horizontal to 45 degrees
below horizontal. The ISO 9000 standard is a little conflicting
(it's still being written): the text says horizontal to 40 degrees,
the diagrams indicated horizontal to 60 degrees.

Vision people (Jim Sheedy, for example, at the Vision Clinic at
UC Berkeley) say the eyes work most comfortably and most efficiently
with about a 30 degree downward cast.

These standards are one reason why I say it's difficult to have
the monitor too low. 45 degrees for most people is buried in the
worksurface.

Chaffin found in 1973 that a 30-45 degree flexed neck posture
caused pain and fatigue but that a 15 degree position produced
no evidence of fatigue after long period. Lee et all (1986) found
a minimal increase in musculoskeletal stress over time for a 25
degree neck flexion, compared to 45 and 65 degrees.

Biomechanical calculations (Chaffin/Andersson 1991, Moroney 1988)
show that neck flexion of 30 degrees produces significant muscle
contractions, but not with less flexion.

Overall the evidence seems to point toward a 15 degree neck flexion
being "safe," 30 degrees being fatiguing, and somewhere in between
is a gray area that no one has researched.

I'm not good at trigonometry. Would somebody figure out how far a
distance it is from horizontal to 15 degrees at about 26 inches?
And to 30 degrees?