Dear Terry and All,
This thought from my 'Rules of Thumb' might be useful.
Reading: � Reading is easy for most people if the letters are 5 millimetres
high at a distance of 500 millimetres; from this we get a ratio of 1:100,
and this will work on any scale. If you are planning a billboard 40 m from a
country road then the letters should be 400 millimetres high (40 m � 100 =
40 000 mm � 100 = 400 mm). Similarly, if you are designing a conference
poster to be read from 2 m the letters should be a minimum of 20 millimetres
high (2 000 mm � 100 = 20 mm).
Cheers,
Pat Naughtin
CAMS - Certified Advanced Metrication Specialist
- United States Metric Association
ASM - Accredited Speaking Member
- National Speakers Association of Australia
Member, International Federation for Professional Speakers
--
on 2002/03/16 09.08, [EMAIL PROTECTED] at
[EMAIL PROTECTED] wrote:
>> Just received an RFP (request for proposal) for a semi-custom terminal
>> from a subcontractor for the US Army. The specs are entirely metric,
>> with one exception: character height on the display is specified
>> at 0.15". All other specs, including mechanical, keypad sizes,
>> temperatures, sealing pressures, etc. are metric.
>>
>> I can't explain the 0.15" (3.81 mm) -- it is not any kind of standard
> for
>> character displays. The ubiquitous 4x20 LCD modules used in these
> devices
>> nearly universally use characters that are 4.75 mm high.
>>
>> I believe the specification is from the Army, and not a metric
> rendition
>> created by the subcontractor.
>
> I should be able to provide you with the answer since it is my field.
> However, I must admit that I am baffled too.
>
> The standard that I would expect to see for this application would be
> MIL-STD1472. It has traditionally dealt with painted labels and the
> version 'F' of the standard gives a range of either 2.5-5 mm or 3-5 mm.
>
> https://www.denix.osd.mil/denix/Public/Library/Ergonomics/milstd-1472.pd
> f
>
>
> A previous version 'D' (which still may be on many bookshelves) gave
> exact values of 2.3 mm and 4.7 mm.
>
> http://jcs.mil/htdocs/teinfo/directives/soft/ms1472d.4.html
>
> However, self-illuminated characters (as on an LCD) do not appear to be
> addressed by that standard and I cannot put my hands on anything
> immediately.
>
> Something that springs to mind immediately is that '15 minutes of arc'
> is a well known (in the human factors community) size for characters.
> Perhaps somebody has done a calculation based on viewing distance and
> worked out a character size using imperial measures. If you get a round
> number in imperial (26 inches is sometimes used) then it will be a
> plausible scenario. I am too lazy to work out the viewing distance for
> 3.81 mm characters and that angular subtense.
>
> There are also some plausible error scenarios where 15' becomes 0.15"
>
> It is also possible that you have been given a legacy size which
> replicates current equipment.
>
> However I would want to see what the standards say for self-illuminated
> characters before sticking my neck out.
>
> The US Army should certainly be using metric measures so there is
> definitely something odd. However, oddities like this no longer surprise
> me. They provide me with food.
>
>
> --
> Terry Simpson
> Human Factors Consultant
> [EMAIL PROTECTED]
> www.connected-systems.com
> Phone: +44 7850 511794
>
