What is the distinction between these two Diablo 1 healing items? They cost the same, but do they recover the same amount of HP? What differentiates them?
The potion of healing restores HP with the following formula:
where the bonus varies with the class, as you can see from the following table:
The HPs are restored immediately.
The healing scrolls instead follow the Healing spell formula:
where the bonuses are the same from the previous table(with the exception of the monk that gets a 2.0 bonus here). The spell level (slvl) is the level your character has learned up to, or 1 if your character has never read the proper book. The scrolls cost no mana, but they remain a spell, so they have a casting time that can be interrupted by melee attacks.
Let's make an example: you have a warrior, level 20, with 200 HPs that has learned level 5 Healing. A potion would give him 50 to 150 HPs, while a scroll would give him 52 to 240 HPs. If instead he had no Healing skill, the scroll would yield 44 to 192 HPs.
Let's consider a sorcerer instead, level 20, 100 HPs and the same level 5 healing. A potion would give him 12 to 36 HPs. With a scroll he gets 26 to 120 HPs. Even with no Healing skill those would be 22 to 96 HPs.
All infos (with the exception of the examples) are taken from the Diablo Wiki