def stell(HDR):
	"""input: HDR_TYPE HDR
	output: int
	Returns the actual position of the data pointer in blocks.
	If an error occurs, function returns -1."""
	
	if HDR.FILE.OPEN != 0:
		pos = HDR.FILE.FID.tell()
		if pos == HDR.FILE.POS * HDR.AS.bpb + HDR.HeadLen:
			return HDR.FILE.POS
	return -1
	#End of STELL