Could I stack it with the Belt of Storm Giant Strength?

In my view no. The book permanently modifies your base strength score and its range. The verbiage of the Belt indicates it changes your strength score. "While wearing this belt, your Strength score changes to a score granted by the belt." The belt will always change your strength score to it, with a caveat. It ceases to work if you meet or exceed that score. So even if it did stack, in that scenario you would suddenly exceed the belt's score by 2, which turns off the belt, then your score drops to its base plus 2, which likely turns the belt back on, fixing your score back to its value.

Wait, why is there no limit? does this mean I could theoretically get a 40 strength? 

Quote from DIemortalscum >>

Wait, why is there no limit? does this mean I could theoretically get a 40 strength? 

 There's technically no limit, but after reading it "The manual then loses its magic, but regains it in a century."

Unless you're a super old living race (elf, firbolg), or have access to time-altering magic/dimensions, you're probably only ever going to access it's magic once. And within a campaign, almost guaranteed that you won't ever get to stage where you're using it twice (unless you have a really long campaign, then all power to ya).

Could make for a great BBEG or NPC though; someone who has lived for hundreds of years and has honed their body to a point where their strength is like, 32 or something.

While that would be the case for the same book, the item isn’t technically unique in the sense that there is only 1 in the world (unless the DM chooses it that way).  There could be 10 of these manuals waiting to be read....each giving it’s magic to the reader.  So, while a single book can only be read once in 100 years....multiple copies could be read within a much shorter period of time.

Or...am I missing something?  Obviously, this is the sort of item that isn’t intended to be abused in such a way, but I don’t know of any rule preventing a character from getting their hands on more than 1 copy of this book within a shorter period of time.

You can even make magic items in dnd, There's a guide in the DMG. But I'm sure the DM would be an ass and say "uh no you can't make magic items"

PC: "why"

DM: "Cause you can't

Quote from WhoStoleRainbow >>

Quote from DIemortalscum >>

Wait, why is there no limit? does this mean I could theoretically get a 40 strength? 

 There's technically no limit, but after reading it "The manual then loses its magic, but regains it in a century."

Unless you're a super old living race (elf, firbolg), or have access to time-altering magic/dimensions, you're probably only ever going to access it's magic once. And within a campaign, almost guaranteed that you won't ever get to stage where you're using it twice (unless you have a really long campaign, then all power to ya).

Could make for a great BBEG or NPC though; someone who has lived for hundreds of years and has honed their body to a point where their strength is like, 32 or something.

Max stat score in 5e is 30 so no you cant go to 40 or 32.

But you can go to 30 

Can you find a definitive claim that the max is 30?

Player's Handbook,       Chapter 7: Using Ability Scores,      Ability Scores and Modifiers

A score of 10 or 11 is the normal human average, but adventurers and many monsters are a cut above average in most abilities. A score of 18 is the highest that a person usually reaches. Adventurers can have scores as high as 20, and monsters and divine beings can have scores as high as 30.

You also have 

Dungeon Master's Guide,    Chapter 7: Other Rewards,     Epic Boons

Alternatives to Epic Boons

Ability Score Improvement. The character can increase one ability score by 2 or increase two ability scores by 1 each. The ability score can now be increased above 20, up to a maximum of 30.

But having read the item description again it seam to break this roles as it increases the max and dos not describe what max or if there is a new one. And as a 700 years old elf could use this item 7 times and wit all the ability's that could make you immortal this is just a broken item. I do not understand why it's not Legendary and I would never encourage anyone to add this in their game as it just breaks everything. A 2 000 year old lich, Druid, Warlock and so on with 40 in every stat and at least +20 to every role for anything is no longer fun. At that point dice are pointless and it's just a game of stats.

If you are going to add it I would STRONGLY encoring modifying it so it no longer breaks the limit. Or maybe a one time use or a longer regain time. Personally I would just not add it or make not break the cap of 20 and defiantly not let it break the cap of 30. Seeing as you can reach 30 from Boons I do not understand why this items was ever even consider okey

Who the **** mad this item. It is so broken

Making it an artifact would be pretty cool 

I think the key here would be to add the limitation that an individual can only benefit from the power of this item once.  After the individual has used the fitness exercises they have improved their body as much as this type of manual (while magical) can manage.

Why is it that out of all the books, this one doesn't have art?

bruh this item doesn't break everything, even if you just add one and a character can somehow live super long to use it multiple times, they'd have to wait 100 years to use it each time.  plenty of time for them to be stopped by someone (maybe the gods themselves) before they become too powerful.  

All the gods including Tiamat should have 100 + in all stats if this items was to make sense. Like what, Gods would not use this item out of principle. And devils and fey creatures can live for a extraordinary amount of time, so again if just on of them got their hands on one of this items they would most likely reach 50 in on stat before any other powerful creatures found out as long as they played it safe.

Some people might think that its fine that gods have 100+ in stats but the gods in the standard DnD is not omnipotent. If that was the case there would most likely only be one not multiple and that god would be abele to folly control every aspect of the world, which at list for me dos not sound like fun gameplay. 

I don't think Gods or any other creature should have full control over the world in DnD as its a game to be played with friends, and that to me seams more fun when there are more options in the world and more possible outcomes to events. All powerful perfect beings with 100 - 1 000 in all stats gives the world les options and fewer outcomes to events.

If you like the items its fine but it is according to the roles the most powerful item in all DnD 5e and the fact that it makes Legendary items and Artifacts lock like trash seam to me like a obvious tell that its broken

Whell a max druid... Lives for thousands of years 

If it had no limit 

Woodbeard     NatureBrand

The lv 20 druid with 80str

The dragon  eater 

Once you start reading the manual, are you the only one that can gain it's bonus then since you started? or could someone also read it at the same time and it would be the first to 48hours?

Quote from DIemortalscum >>

Wait, why is there no limit? does this mean I could theoretically get a 40 strength? 

 yes

Quote from McCoy_Keith >>

While that would be the case for the same book, the item isn’t technically unique in the sense that there is only 1 in the world (unless the DM chooses it that way).  There could be 10 of these manuals waiting to be read....each giving it’s magic to the reader.  So, while a single book can only be read once in 100 years....multiple copies could be read within a much shorter period of time.

Or...am I missing something?  Obviously, this is the sort of item that isn’t intended to be abused in such a way, but I don’t know of any rule preventing a character from getting their hands on more than 1 copy of this book within a shorter period of time.

 produce ing them would be my way to go about abusing this

I would argue you can only benefit from this item once, for obvious game balance reasons.  No clear rule covers it, but that interpretation is in the "spirit" of a couple of rules.

From XgtE: Introduction: 

Combining Different Effects

"Different game effects can affect a target at the same time. For example, two different benefits can give you a bonus to your Armor Class. But when two or more effects have the same proper name, only one of them (the most powerful one if their benefits aren’t identical) applies while the durations of the effects overlap."

In this case, the duration is permanent.  But it is still an effect from the same item, thus the same proper name.

From DMG: Magic Items: Attenment:

"Additionally, a creature can’t attune to more than one copy of an item. For example, a creature can’t attune to more than one ring of protection at a time."

Obviously, this isn't an attuned item.  But further support for a general rule of not duplicating the same effect being a general game rule.

Quote from Glaldrumin_Hornbane >>

Could I stack it with the Belt of Storm Giant Strength?

 

 No. The Belt of Giant Strength doesn't increase your Strength score, it overwrites it. The Manual checks your *original* Str score, before equipping the Belt, and *that's* what gets buffed. That total will almost certainly be lower than the 29 from Storm Giant Strength, so the Belt will reset your Str back to 29.