Abstract: This invention relates to a method of testing an n-bit programmable counter. It is desired to test the n-bit programmable counter in fewer than 2.sup.n cycles. Accordingly, a counter value output on the counter is coupled to a variable increment rate input on the counter. Each bit of the counter is reset to a binary 0 initial state. A binary 1 state is loaded into a carry-in bit of the counter and the counter is iteratively doubled, by means of the coupling between the counter value output and the variable increment rate input, until a carry-out bit of the counter assumes the binary 1 state to thereby allow the counter to be fully tested in n+1 iterations. The counter value output and the variable increment rate input are decoupled from the counter when the counter is not being tested. The counter is provided with a parallel load input to allow simultaneous resetting of each bit. Intermediate counter values may be checked to provide a means for localizing errors within the counter.

Abstract: A slip gripping mechanism is shown for supporting a string of cylindrical conduit within the interior bore of a circumscribing conduit. An elongate body has a plurality of spaced longitudinal slots at one end. Vertically shiftable slips are carried in the slots by side edges which engage mating profiles formed in the slots. The slots form guideways for the slips for shifting the slips upwardly and outwardly relative to the body between a set position engaging the circumscribing conduit and an unset position. Each slip has an arcuate lower surface and a selected width to thickness ratio to allow controlled flexing of the slip in the direction of the circumscribing conduit as the slip moves to the set position.