A simple method, based on Back Scattering (BS) measurements, has been used to calibrate the analysing magnet of the Folded Tandem Ion Accelerator (FOTIA). The combination of various beams with different charge states and at different terminal voltages covering a range of magnetic fields has yielded the calibration constant ‘K’ of the magnet with an estimated error of about ±:1% The resonance in ¹²C(p;p)¹² Cat E^p _lab=4:808 MeV (the excited state, 5/2⁺ ;of ¹³N with a width of 11 keV) has also been measured. The  ‘K’ value determined from this is consistent with that  obtained using BS.