" Morales states that Barrios had a peculiar method of practicing:  he had a
small sack filled with 100 pebbles.  He would
commence to play a piece, and if he finished it with no errors, a pebble was
taken out of the bag after which the piece would be played again.  If a
mistake was made, he would put all the pebbles back into the bag and start
over.  He would thus continue until he had played the piece without error 100
times consecutively."

Six Silver Moonbeams, The Life And Times of Agustin Barrios Mangore
by R. Stover
Page 173.

Sila Godoy played over 80 compositions from memory.  At the age of 62 in
preparation to record, played those works
25 times consecutively without error, daily.  This I witnessed.