This 9 Pin bias probe is a single head unit that must be used in conjunction with a multimeter. This probe takes a direct DC plate current measurement by breaking the plate connection (pin #7). It does not use a reference resistor and it is not in the cathode connection. This means you do not have to compensate for screen current or any other variables.
Made from a custom tooled delrin body with a Belton 9-pin socket and hardened Deutsch pins