of a desired placement of a ball not shown and a ball seat not shown to receive the ball to thereby isolate a zone 50 that is deeper in the well than the ball seat i e to the right from a zone 51 that is shallower in the well 20 than the ball seat i e to the left it will be understood that the ball and ball seat are to be placed in a portion of the casing 62 that lies within the targeted geologic formation 24 and that the pressure at any given location within the well 20 is approximately equal to the pressure at a wellhead 49 at the surface 21 plus the product of the vertical elevation change 46 times the density as measured in units corresponding to the unit used to measure depth of a fluid residing in the well 20 assuming that the well 20 is filled with the fluid fig3 is a sectional elevation of an embodiment of a ball 10 of the present invention received in a ball seat 44 that has been previously set within a section of a casing 62 of the drilled well 20 not shown in fig3 illustrated in fig2 to create an isolating seal it will be understood that a number of tools exist for setting the ball seat 44 within the portion of the casing 62 in.