You calibrate a water brake dyno with an arm of a known length and accurate weights. For example, if you are going to make 600 lb/ft torque and your arm is 3 feet long then you need to put 200 pounds of weigh in the arm set the software. Arm length and actual weight is critical. If you have an arm that is 22 inches and you tell the software the arm is 24 inches you induce an error into the calibration. Same with the weights. If you are telling the software you are putting 200 pounds on the arm it needs to be 200 pounds. And you should get 2 sets of numbers off the dyno. The actual numbers the engine produced at the brake and the corrected numbers that correct to a standard. That’s because you can dyno the same engine in August on a 100 degree day and again in February on a 40 degree day and get the same corrected numbers. The uncorrected numbers will follow the weather but the corrected number should be the same no matter the weather.