Parley promotion mechanism for vocabulary

[Hartmut Riesenbeck]

Hi Jürgen

I try to bring some light into parleys grade handling as far as I understand 
it from reading the source code.

There are two levels -  pregrades and grades. If you type in a brand new 
vocable both are 0. If you answer the right translation at the first time, it 
is assumed that you know the vocable already ant it is set to grade 2.
If you fail the first time and enter the correct answer at an later attempt, 
it is set to PREgrade 1. The pregrade blocking times are very short and not 
configurable. 

Pregrade  1 -> 3.5 minutes
Pregrade  2 -> 7 minutes
Pregrade  3 -> 15 minutes
Pregrade  4 -> 1 hour
Pregrade  5 -> 2 hours
Pregrade  6 -> 4 hours
Pregrade  7 -> 8 hours

After you finish pregrad 7 the vocable elevate to the the grade level. Which 
starts at grade 1 and ends with grade 7. The blocking times for the grade 
levels are configurable in the lessons configuration dialog. If you don't 
practice a vocable for some time, its grade is decreased by one. This time 
period is also configurable in the lessons configuration dialog. 

I think the distinction between grade and pregrade was made to keep 
compatibility with older versions of parley, which only know grades. You can 
find out if are at grade or pregrade level if you look in the upper right 
corner of the practice window. The word "initial" before the grade number 
means pregrade and the words "long term" means grade level.

I hope that helps.

Best regards
Hartmut