If you have low evade for example 12 points; after chipin 49 ped implant you got more then 3500 points, and you unlock hiden Avoidance skill. Avoidance unlocks when you reach a professional standing of level 25 Evader level. A measure of your ability to avoid some attacks. This increases the defense and helps to safe armor declay and keep HP.
Example: ff you have only 2 points of Diagnosis skill after chipin 19,44ped implant you got more then 2500 points, and you unlock hiden Medicine skill. This is a composite measure of all your medical skills. Medicine unlocks when you reach a professional standing of level 20 Paramedic.
IF you buying both skills I applied a big discount.