One of the spells allowed to clerics is Ironskin. While reading it I feel like its math is not correct.
You gain a +4 enhancement bonus to your existing natural armor bonus (if you do not have a natural armor bonus, you are considered to have an effective natural armor bonus of +0).
This enhancement bonus increases by 1 for every 4 caster levels above 4th, to a maximum of +7 at 15th level.
So it grants you a +4 to +7 bonus to your natural armor bonus; this is good. What does not make sense is that for every 4 caster levels above 4th you gain another +1 but it caps at CL15.
- CL 4–7 is +4
- CL 8–11 is +5
- CL 12–15 is +6
- CL 16–19 is +7
The reason why I chose to have CL4 included is because of the CL15 explanation. I feel like the following is more reasonable as it makes better use of your total caster levels and is more correct about being 4 caster levels above 4th:
- CL 5–8 is +4
- CL 9–12 is +5
- CL 13–16 is +6
- CL 17–20 is +7
So with there being a mistake in the presentation of the spell (I only have access to the online source and can't check the printed version) how should the spell be used?