Now, one thing we have known that whatever arrangement you make, this tow hook, how do I apply the pull? It must be applied from top somewhere- is it not? So, what we have is what is called a resistance dynamometer and this resistance dynamometer is a device which is helped by a carriage on top of the model, the carriage being held separately on rails mounted on the towing tank. So, the carriage and model have no connection except through the dynamometer. Now, dynamometer is held by the carriage
and it has a pillar, which moves inside the dynamometer, this pillar is fixed on the model. So, model takes the pillar, but not the dynamometer, the pillar is free to go up and down in this thing.