detecting {HEAD ~ positions} of the image bearing belt using a first sensor and {TAIL ~ a second sensor} disposed in a different position from that of the first sensor; and 
detecting { HEAD ~ positions } of the image bearing belt using a first sensor and { TAIL ~ a second sensor } disposed in a different position from that of the first sensor ; and
OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH REL OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH