To what chart are you referring?. .. .If you want to be able to calculate the assumed temperature, you would need the OAT, QNH and A/C gross weight. Therefore, there is not normally a 'chart' as such, because the assumed temperature calculation is based on actual conditions, in conjunction with the airfield data.. .. .Most airlines produce their own performance manual containing all the data needed to calculate this, given the above parameters.. .. .Can you be more specific about what chart you are after?