I log my practicing using a very simple method. I get a piece of grid paper (though you could use a spread sheet computer software) and list all of the pieces I am currently working on over in the RH side of the paper. Each paper will be for one month at a time. Across the top of the paper, I will put the dates (1-- whatever) for the month. This sheet is used simply to tally the days that I practice each piece, and I mark an "X" wihtin the coordinate box for each day that I practice each piece. I have attached a copy of this as I do it :

I also keep a practice
journal. This is a little more detailed, and it is meant to keep track of exactly what I practice. An excerpt from a page may look something like this :
BachG Major
Prelude : Entire thing, 3 times from memory, up to tempo
Fugue : SV (1-23)(24-38)(38-46)(46-51)
{ MV (5-81)(81-82)(83-85)(85-86)
{ BV (11-21)
I have a little system that gives me information. For example, I practice in 15 minute sessions (I actually use a timer). Each line used to record my practice chunks is representative of a single 15 minute session, unless bracketed with another line. As in the case of the Bach Fugue, the SV stands for soprano voice, and MV middle voice, BV bass voice. As you can see the MV and BV are bracketed together (as best I could on the computer), meaning I practiced those within the same session. Also, each set within the parenthesies means that I practiced that particular chunk 7 times in a row, as a chunk.
I know how many hours I have practiced based on the amount of 15 minutes sessions I have done. I just do the math in my wee little thinker.
I hope that helps

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m1469