errors

• there could be distractions so use earmuffs to remove noise distractions
• there is a difficulty in deciding distance on ruler if between measurements so be consistent, either use top or bottom of the finger to decide distance
• the ruler could hit the hand on the way down so have finger and thumb far enough apart to reduce likelihood of ruler hitting hand as it falls
• the person may improve with practice so leave gaps between tests to reduce the effects of practicing