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The following changes were made to keep your vehicle’s performance more effective throughout the course of the battle:
Effectiveness of damaged engine has been increased from 50% to 60%
Knocked-out Crew members’ effectiveness has been increased from 0% to 20%
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The question is about jack of all trades (JOAT) and whether the bonus is cumulative, takes the highest or if it overrides the 20% base value.
Cumulative seems the best value for the skill and I would hope this is the case.
one crew mate is knocked out does it bring that skill up to 50% or 70% ?
two crewmen out now is it 25% or 45%? and if you are only gaining 5% ... thats really not effective
three are out... 12.5% if JOAT overrides the value (bad), 20% if it takes the highest, or 32.5% if they are cumulative.