A leather-bound book with the title Ability Training Manual inscribed in gold inlay along with its type:

(Strength/Dexterity/Constitution/Charisma/

Wisdom/Intelligence)

Value: 200Gp

At the start of a long rest, decide how many hours you wish to spend studying the book.

Make a skill check for the skill you wish to study, the DC is you skill score +1, on a fail, you still spend the time studying, but gain no points towards levelling up that skill (NOTE: Your skill modifier can be used in the roll)

Then

Roll 1d10 for each hour you spend studying and add up the total.

Totals carry over between study sessions.

Once you reach enough points, the total resets to 0 and your score for the ability studied increases by 1, any excess points are carried over to the next study session.

Changing the ability you are studying between sessions resets all progress towards the ability you were studying before.

To calculate how many points you need to level up, take your skill score + 1, then multiply by 10.

Example To level up charisma from 15 to 16:

15 + 1 = 16

16 x 10 = 160 points.

If the book is lost or destroyed, all progress towards that ability study is lost.

Each book only contains the material required to study 1 ability.  You will need to buy all 6 to study all 6 abilities.

 -Example-

Sky wants to spend 4 hours studying charisma while her non elvish party members sleep.

She currently has 15 charisma.

She needs to roll 16 or higher to focus on her studies

She Rolls 1d20 and adds her modifier for a total of 17.

As this is higher than the DC, she is now fully focused on her studies.

She has studied charisma previously and has 154 of the 160 points She needs to increase from 15 to 16.

She rolls 4d10 for and gets 22.

Now She has attained the required 160 points, her Charisma skill increased from 15, to 16.

Her point total resets to 0, and the excess points from her study session, in this case 18, are put towards her next charisma study, for which she will need 170 points.

She makes a note of her points 18/170 for next time.

-Example 2-

Grog wants to study Intelligence for 2 hours.

He currently has 9. 

He rolls a 1d20 and adds his modifier, unfortunately its a very bad roll, only 7 total.

He spends 2 hours studying but can't fully focus on his studies and gains no benefit from studying. 

-Important Notes-

This book increases your skill score, NOT your modifier.

The book can be traded between players, but you loose your progress towards the next level, same as if the book was lost or destroyed.

-OPTIONAL RULES-

Exhaustion: 

If your DM is using 'exhaustion rules' take this into account when deciding how long to study for, studying is not a substitute for sleep.

Single Use:

Your DM may opt to make this item single use, Once you have enough points to level up a skill, you have learned all this book can teach you and will need to buy another to keep studying, the book becomes worth half its value for resale.