it is noted that the push rod 24 and bellows 26 is an exemplary mechanism to provide the pressure induced force on the fiber illustrated by arrow 30 such force 30 bends the fiber 10 placing exemplary grating 16 in tension and exemplary grating 18 in compression differential measurements in core 12 and 14 may then be taken to sense the pressure change it is noted that not only are drift factors eliminated due to the collocated nature of the core measurement portions e g gratings written during fiberization in multiple cores of a multi core fiber but temperature effects are also eliminated due to the nature of the multi core system in another exemplary embodiment the multi core fiber comprises at least two cores that have the same doping to minimize differential reactions to pressure in another embodiment at least two cores are reflective to the same wavelength referring now to fig3 a cross sectional plan view of an exemplary multi core fiber 10 is illustrated as being actuated by a push rod 24 and diaphragm 32 other than use of the diaphragm 32 instead of the bellows 26 operation of the collocated sensor system is identical to that described above with regard to fig2 it should be noted that any mechanism effective to transmit a force representative of pressure against the fiber is contemplated herein the bellows and push rod and diaphragm and push rod embodiments being merely exemplary referring now to fig4 a cross sectional plan view of an exemplary.