If I wanted to switch from fabled tracking (about 0% fabled), to necromancy, how many lessons would I retain?

Don't know how to figure it out myself

9.0.10 LESSON POOLS

To see how many lessons are in your lesson pools:
Syntax: LESSONS

To transfer lessons between pools:
Syntax: LESSONPOOL TRANSFER LESSONS FROM TO

Lesson pools come into play when an adventurer chooses to change skills or
specializations. By 'forgetting' a skill or specialization in order to
learn another, all lessons placed into that skill are dropped into the
connecting lesson pool at a 20% loss. So if you had spent 100 lessons in
Aquamancy and decide to forget the specialization, you will move 80
lessons into the Mysticism Pool (losing 20 lessons irrevocably). These 80
lessons may only be used on skills that connect to that lesson pool.

If you transfer lessons between sibling lesson pools, there will be a
further 20% loss of lessons. For instance, transferring 80 lessons from
mysticism to spirit will have a net loss of 16 lessons in the transfer.
Sibling pools share the same parent lesson pool (i.e., spirit and
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mysticism pools share the mind pool).

Finally, transferring lessons from a secondary (or sibling pool) to the
parent will have a further loss of 30% of the lessons transferred, so
transferring 80 lessons from the mysticism pool to the spirit pool will result
in a net loss of 24 lessons. There is no lesson loss when transferring
lessons among the parent pools (i.e., body, empathy, mind, artistry, and
spirit).

Therefore, if you quit the Aquamancy Guild and join the Geomancy Guild,
you may now use those 80 lessons on the Geomancy specialization (or any
other skill that flows from the Mysticism Pool). If you decide you do not
want to use any of these lessons on any skill that flows from the Mysticism
Pool, you may drop the lessons into the root at an irrevocable 30% loss
(so the 80 lessons in the Mysticism Pool will drop to 56 lessons in the Spirit
pool. These 56 lessons can be moved to any root at no further lesson loss,
so for all practical purposes may be used to learn any skill at no further
loss.

Be very aware that there will be very light lesson penalties for those who
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make small adjustments to their skills (like a warrior deciding to change
from the Bonecrusher specialization to Blademaster specialization), but
drastic changes will be quite traumatic and costly (like a warrior
deciding to quit knighthood and become a mage).

See also LESSONS, FORGETTING SKILLS, LEARNING.

how many lessons to fabled, then?

Skilllevel Number of lessons Total
---------- ----------------- -----
Inept - Novice 0007 lessons 0007
Novice - Apprentice 0009 lessons 0016
Apprentice - Capable 0018 lessons 0034
Capable - Adept 0055 lessons 0089
Adept - Master 0089 lessons 0178
Master - Gifted 0111 lessons 0289
Gifted - Expert 0134 lessons 0423
Expert - Virtuoso 0177 lessons 0600
Virtuoso - Fabled 0312 lessons 0912
Fabled - Mythical 0380 lessons 1292
Mythical - Transcendent 0423 lessons 1715

912 lessons, so if they were in the same lessonpool, 729. If they are in sister skillpools, then 583. If they aren't, then 510.

Got it. This can be closed, if a mod wants to.

quick questions how do you transvere lessons back to the main pool, meaning i want to take all the lessons i have in body and put it in the main pool not a sibling pool?

If they are in body, then you're fine. You can transfer them for free wherever you need them. You can't actually transfer them to the main pool, but they essentially are there.