All charges submitted by a critical access hospital (CAH) will appear under one of the following types of bill (TOB): TOB. Definition. 11X. Inpatient. 12X. Inpatient ancillary. 14X. Non-patient diagnostic. 18X. Swing-bed. 85X. Outpatient. The third digit of the TOB is the bill frequency. This digit shows the nature or intent of the bill submitted..