This article is from the Piano Playing from Memory FAQ, by Isako Hoshino rmmpfaq@yahoo.com with numerous contributions by others.
The use of difficulties as described above in 3.10 can be a basis
for testing how well you have memorized. Here are a few more
possible tests. (You may think of others.) Note that none of
these is an absolute indicator, but they may be useful gauges
depending on your particular abilities.
* Can you sing or hum all the right notes?
* Can you play the piece v-e-r-y slowly?
* Can you make all the right finger motions while pretending
to play the piece on a table top?
The ultimate test is how you play the piece in a performance
situation. The presence of an audience may cause you to play a
piece which you have worked on for four months as if you have
worked on it for only two.
 
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