measuring of a first probe pressure p pr1 the pressure measurements can be implemented in the manner previously described next the arrow 550 represents the change in borehole pressure which as noted above can occur naturally in certain circumstances or can be achieved by pumping on the well or by the previously described technique of local pressure modification the block 530 represents measurement of the second borehole pressure pbh2 and the block 540 represents measurement of a second probe pressure p pr2 then the block 580 represents computation of the true formation pressure using the measured pressures and equation 5 above and the block 590 represents reading out of the true formation pressure in the routine represented in conjunction with the diagram of fig6 several pressure measurement pairs p bhk p prk are utilized to determine the relationship therebetween and extrapolation can then be used to determine the true formation pressure an index k is initialized at 2 block 605 and the blocks 610 and 620 represent the measurement of the first borehole pressure p bh1 and the first probe pressure p pr1 as in the corresponding blocks 510 and 520 of fig5 also as in fig5 the arrow 550 represents a borehole pressure change whereupon.