Based on what you and Thibaud said, I'm going to make a linear graph
relating distance to character size. It will have three lines: maximum size
(1/100) and minimum size (1/200) and average size (1/150).
Thanks!
John
----- Original Message -----
From: "Patrick Powers" <[EMAIL PROTECTED]>
To: "John Carmichael" <[EMAIL PROTECTED]>
Sent: Thursday, June 02, 2005 11:25 PM
Subject: Reading at a Distance
Message text written by "John Carmichael"
For example, if you are designing a sundial for a tall tower and you know
that it must be readable from a distance of 100 meters, how tall should the
numerals be?<
Hi John. I have always thought there are two aspects here. These are the
minimuum size of letter that can actually be read and the actual size
chosen because of balance in the design of the dial. The latter is
dependent on one's artistic abilities but the former can be calculated.
There is however a difference between what can be read and what is easily
read.
All you need to do is look at the size of text which can easily be read at
arms length even by those with slightly imperfect vision. My rule of thumb
in this has usually been that lettering of between 2 and 4mm in height and
held 40cms away represents these two aspects. Thus 2mm text is readable
but needs some concentrateion whereas letters of 4mm in height stand out
more. These two rules of thumb (conveniently) imply ratios of 1:200 and
1:100
To answer your question about a dial readable at a distance of 100 metres -
along the line of sight - then this would suggest that the minimum
character height should be 50cms but that if it were necessary to have
fairly easy readability at that distance then the minimum letter height
should be 100cms. All this adjusted to the designs of the dial of course
and one needs to remember that such a large dial as is implied by
readability at 100 metres may look unbalanced close up.
Does this help?
Patrick
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