1. A computing system comprising: at least one computing device having at least one controller, the at least one computing device configured to tune each gas turbine in a set of a plurality of gas turbines based upon a power output parameter and an emissions parameter, wherein the at least one computing device is configured to: model each gas turbine in the set at a respective base load level based upon a respective measured ambient condition; command each gas turbine in the set to adjust a respective actual value of the power output parameter of each gas turbine in the set to match a respective scaled value of the power output parameter of each gas turbine in the set, wherein the respective scaled value of the power output parameter is equal to a fraction of a difference between the respective actual value of the power output parameter and a nominal value of the power output parameter of the set, and measure a respective actual value of the emissions parameter for each gas turbine in the set during the adjustment of the respective actual value of the power output parameter; and perform an adjustment to a respective operating parameter of each gas turbine in the set based upon a respective scaled value of the emissions parameter of each gas turbine in the set, wherein the respective scaled value of the emissions parameter is equal to a product of an emissions scale factor multiplied by a difference between the respective actual value of the emissions parameter and a nominal value of the emissions parameter at the respective measured ambient condition for each gas turbine in the set, wherein the adjustment to the respective operating parameter of each gas turbine in the set aligns each gas turbine in the set onto a first line in a graphical space plotting the power output parameter versus the emissions parameter, wherein the first line is orthogonal to a characteristic line in the graphical space, wherein the characteristic line is a mean characteristic line of all of the plurality of gas turbines in the set, at the respective base load level of each gas turbine in the set, plotting the power output parameter versus the emissions parameter.