length and weight it is supported on an armored cable known as a well logging cable suitable electrical conductors are enclosed in the cable the cable being identified by the numeral 16 the cable extendes to the surface and passes over a sheave 18 the cable 18 is stored on a drum 20 the cable might be several thousand feet in length to test formations at great depths conductors from the cable 16 are connected with various and sundry controls identified at 22 the electronic control equipment for the formation tester is provided with power from a power supply 24 the signals and data obtained from the formation tester 10 are output through the surface located equipment and to a recorder 26 the recorder records the data as a function of depth an electronic or mechanical depth indicating mechanism is connected to the sheave 18 and provides depth measurement to the recorder 26 and is thus identified by the numeral 28 refering now to the tool body it will be first observed that it supports a laterally extending probe which is identified by the numeral 30 the probe 30 has a piston which extends it from the tool body the extended probe is surrounded by a ring of elastomeric material 32 the ring 32 is a seal pad it is pliable and is affixed to the probe 30 for sealing operation moreover the ring 32 operates as a seal when pressed against the adjacent.