First of all, the way HIT POINTS VALUE (HPV) - are calculated in Powers & Perils is beautiful and highly reasonable, unlike the way they are calculated in AD&D:
HPV= Strenght value + Stamina value (which is the same as Constitution in AD&D) + Constitution value (which represents the physical health of a character) / 4
so, to sum it up:
HPV= (S+St+C) /4
Then you have to take into account DAMAGE TOLERANCE VALUE:
((C/20) +Stamina bonus) x (-1), round up.
You usually end up having a DTV of -3, -4 or something like that.
Last, you calculate your Lethality index.
Each character has a Lethality Index. The value = DTV * 4. If your DTV
is -4, your LI is -16.
Effects are as follows:
Between 0 and DTV - The character is limited and semiconscious. He may take
one action per tactical turn OR move MR/10 (RU) in a tactical turn.
When less than DTV and not less than LI - The person is unconscious.
Less than LI - Dead.
When a wound is suffered that leaves the character with an HPV value
less than ONE, a roll is taken on the Death Table, (a sort of "critical hit table") so that if you are unlucky and roll a 20, you can instantly die (head severed, for example). But this dpends on the potency of the blow received.
If, for instance, you received a severe or DEADLY blow, it is likely you will die if you roll on the DEATH table.
So, to sum up: you calculate your HPV, then DTV and your LI value.