The effect described is for each skill level added.
Towers
Gun, Missile and Laser
Adds 10% damage.
No max level.
EMP
Adds 10% slow and 10% time.
Max level: 10.
Technology
Shock missile
Converts 10% damage from the missile tower’s total damage to shock damage.
Max level: 10.
Fire laser
Converts 10% damage from the laser tower’s total damage to fire damage.
Max level: 10.
Player
XP and Money
Get 3% more from every ship that is shot down.
No max level.
Starting money
Get 50 extra money at the beginning of each level.
Max level: 10.
Luck
Adds 10% chance to find artifacts.
No max level