This article is from the Piano General Topics FAQ, by Isako Hoshino rmmpfaq@yahoo.com with numerous contributions by others.
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[7] How Do I Represent Notes Using "Text" Characters? (Piano)
There are three major notation systems being used rather
frequently today. When you see a notation on your screen,
you will have to judge for yourself which system is being
used. In most cases, that shouldn't be too difficult. For
instance if you see "RPT" written after the poster's name,
you can probably assume they are using the "piano technician"
notation (RPT = Registered Piano Technician). And if you
start seeing numbers higher than "7" being used after the
pitch, you probably can assume the "MIDI" notation system is
being used.
 
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