The 33% skill increase was taken from the total tt skills from the ES100 stand point. Calculated as, total tt skill gain is (ES100-ES500)/ES100 = (0.75-1.00)/0.75 = -0.25/0.75 = -0.33.. So, if you use the ES100 you will gain 33% less skill (based on what you have) than if you burned the same...