Okay let me see if I've got this. Sorry for all the questions but I am terrible with even basic math. To keep things simple I'm going to start with maximum hit points at level 1 and use an average number of 4 for each new HD. So for an Elven F4/MU7 with no constitution bonus I came out to 20 total hit points. I always added at least 1 hp per level gained as you suggested. Is my math right?
Using Gygax's version of 9HD+5 using the same parameters above I get 43 hp divided by 2 = 21.5. So more or less the same.
The Elf
Re: The Elf
No I think that is incorrect. Because you are keeping the prior total if higher at each level gain, you have to step through each level one at a time. For levels 4/7, you end up with 28hp if you assume rolling 4 at each fighter level and a minimum gain of +1 at each MU level (21 HP by the time you reach fighter level 4 and +1 at each MU level = 28 total, assuming you advance to level 4 fighter before gaining any MU levels).
Re: The Elf
Ah okay. Yea I was bouncing back and forth and leveling up whichever class would come up next.
Level 1 Fighter = 8hp
Level 2 Fighter +5hp = 13 hp
Level 2 Magic User +1hp = 14hp
Level 3 Fighter +4hp = 18hp
Level 3 Magic User +1hp = 19hp
Level 4 Fighter +4hp = 23hp
Level 4 Magic User +1hp = 24hp
Level 5 Magic User +1hp = 25hp
Level 6 Magic User +1hp = 26hp
Level 7 Magic User +1hp = 27hp
But I don't understand why you wouldn't get a full HD (4hp) at level 7 since you your HD total goes from 4 to 5.
Level 1 Fighter = 8hp
Level 2 Fighter +5hp = 13 hp
Level 2 Magic User +1hp = 14hp
Level 3 Fighter +4hp = 18hp
Level 3 Magic User +1hp = 19hp
Level 4 Fighter +4hp = 23hp
Level 4 Magic User +1hp = 24hp
Level 5 Magic User +1hp = 25hp
Level 6 Magic User +1hp = 26hp
Level 7 Magic User +1hp = 27hp
But I don't understand why you wouldn't get a full HD (4hp) at level 7 since you your HD total goes from 4 to 5.
Re: The Elf
5HD x 4 = 20, which will be less than the 26hp you have being levels 4/6, so you get the minimum gain of +1.
Re: The Elf
Okay I think I have it. So if the current class that is leveling up would have less HD then what you currently have you only gain 1hp. So even when the Elf reaches his level maximum of 8 as a Magic User he would still only gain 1hp because 5+1 HD (22) is less than 27. Wow I don't know why my brain has a hard time processing this. Since the rules never explain this how did people back in the day figure this out?
Re: The Elf
I think they didn't - at least Gygax's divide-by-two method is not mentioned anywhere in the original books, so I guess most people either made it up or wrote letters to TSR asking for guidance (Gygax mentioned how he handled Elves in the Dragonsfoot forums).