Something like this should work so you don't alter your index variable.
Code:
main:
  for Measurement = 0 to 17
      gosub DwellTable
  next Measurement
  goto main
 
DwellTable:
  IF Measurement > 5 THEN Dwel2
  lookup2 Measurement,[$0110,$0120,$0130,$0140,$0150,$0160],dacdwell
  RETURN
 
Dwel2:
  IF Measurement > 11 THEN Dwel3
  lookup2 Measurement-6,[$0111,$0121,$0131,$0141,$0151,$0161],dacdwell
  RETURN
 
Dwel3:
  lookup2 Measurement-12,[$0112,$0122,$0132,$0142,$0152,$0162],dacdwell
  RETURN