the power supply the closed switch and the resistors before that switch the remaining resistors after the closed switch being by passed the ammeter therefore measures current through the resistors prior to the closed switch and can be so calibrated to indicate or identify the particular switch or yarn member directly thereon so the operator can identify the troublesome yarn with this arrangement when a switch is closed by the action of the plunger 54 the current through the resistors preceeding that switch is displayed on the ammeter 70 current does not flow unless a switch is closed for example assuming there are 1 000 needles and yarns and a known voltage of 100 volts is applied to one ohm resistors the current read by the meter 70 is determined by ohms law and is therefore determined by the number of resistors preceeding the closed switch thus each switch is indicated by a particular reading and the meter can be so calibrated in this example closing switch sw 1 would record 100 amps closing switch sw x would record 0 1 amp the ammeter can therefore be calibrated accordingly thus when the tension in a particular yarn becomes too great thereby closing a switch the current through the resistors could be read directly on the ammeter as a particular yarn number the operator would thereby know which yarn creel or tube to.