The AdirPro Prism Pole Level With 40 Minute Vial is a prism pole level, fastening it to the pole will assist you in determining that it is erected perfectly upright. It is available for 1 1/4 in (32 mm) poles and 1 ½ in (38 mm) poles.
A 40 min. vial is a less sensitive leveler than the 20 min. or 8 min. it would be best for projects that involve holding the pole by hand thereby providing accuracy for extended time, whereas the other vials though they are more accurate won’t be able to provide the best in areas with lots of vibrations such as near roads or at construction sites, therefore in those areas it would be best to use a 40 min. vial.