Still more expeditious is the use of a planimeter, such as Captain Prytz's " Hatchet Planimeter," which yields fairly accurate results, or G.
Coradi's " Polar Planimeter," one of the most trustworthy instruments of the kind.'
Tennant, " The Planimeter " (Engineering, xlv.
These theorems may prove useful in preliminary calculations where the pressure-curve is nearly straight; but, in the absence of any observable law, the area of the pressure-curve must be read off by a planimeter, or calculated by Simpson's rule, as an indicator diagram.
The construction of a second funicular may be dispensed with by the employment of a planimeter, as follows.