I happened to be at home when I read this and thus had access to
some different references.  Scott Mueller, in an old edition of
Upgrading and Repairing PCs, gives the horizontal frequency for
the Monochrome Display as 18.432 kHz.  At this point, I'm
inclined to believe that the IBM figure is incorrect.  I'd like
to apologize to the list for first publishing that figure and
hope that I qualified its source sufficiently so that people could
use the information in my post with a cautious and critical eye.

>On 18 Jul 98 at 6:27, Neal Daskal wrote:
>
>> My source is a IBM publication, PC and PS/2 Pocket Reference Manual
>> S41G-5086-00.  I quoted from it to try to answer the original question.
>> Of course, it may be wrong even though it's IBM.  Wouldn't be the
>> first time.  Also note that the value I quoted is described as the
>> "Sync Freq".  Could that be different from the scan frequency?
>> Anyway, to add perspective I've added the values given for the
>> IBM Color and Enhanced Color Displays below.  I interpret "EGA/CGD"
>> to mean "Enhanced Graphics Adapter set up to use the Color Graphics
>> Display".
>>
>> >On 17 Jul 98 at 12:05, Neal Daskal wrote:
>> >
>> >> 5151  50/16.257khz  Mono
>>    5153  60/15.750khz  Color
>>    5154  60/15.750khz  EGA/CGD
>>          60/21.8khz    EGA/EGD
>> >
>> >  The PC video FAQ I found shows 18.43kHz horizontal for both MDA and
>> >CGA, but I could've sworn that CGA was 14.something -- in that
>> >awkward range where most men can't hear it, but most women can (and
>> >find it irritating).
>
>  So over the weekend I dug out my IBM Technical Reference (revised
>ed, 1984)[*], which confirms the 15.75kHz for the Color monitor (at
>50 or 60 Hz) -- the web site that showed it as 18.43kHz was
>apparently incorrect.
>  But it DOES show 18.43@50 for the Mono Display horizontal scan
>frequency.  It shows 16.25MHz (that's MEGA, not KILO) as the total
>"throughput" for the display monitor.
>
>[*] This edition lists three display options:  Mono, CGA, and the
>display in the IBM Portable PC.
>
>  I am unable to find a spec printed on my mono monitor here, or a
>URL for its manufacturer.
>
>David G