A Charm is an Occult Trinket – a lesser power form of a Talisman. The charm is the least powerful type of Trinket. Learning the magical arts is not necessarily easy. Many masters begin their students with minor tricks of prestidigitation and the like. A practitioner of magic can both learn rote formulae and improvise ones from a greater body of knowledge to create charms. Charms follow the standard patterns and practices to create Empowered Occult Items.
Rote Charms: A magus can potentially perform minor variations to rote charms. These variations are in form only and do not affect the actual effect of the charms. The magus’s Magic Aptitude dictates the ability to tweak a rote charm. Only a magus, a character skilled in a Tradition/Methodology/School, can tweak rote charms.
d20 [specific] Crafting Requirements: Occult Aptitude 1 OR 3 [Occult] Allotted Essence. The spell Detect Magic, a Mana Pool, class: Wizard
These types of trinkets can contain no more power than granting a +1 on Spell Attack or Increasing a Spell Save DC by 1; it can impact spell initiative or effective level by no more than 1. Conversely, it can grant no more than +1 on checks to resist (base Ability or specific Save) effects, or +1 on Skill/Lore checks. It can augment a Mana Pool no more than 2.
Attunement
Aptitude
Command Word vs. Empathy [trigger]
Mana vs. Self Fueled
Like formulae these charms correspond to particular schools, methodologies, and styles.
There are many Occult Models to serve as an example.