Graticule and Uncertainty

• The eyepiece graticule is a glass disc with a scale etched on. It is inserted into the barrel of the eyepiece.
• The eyepiece graticule first needs to be calibrated for the objective lens you are using.
• The eyepiece graticule and stage micrometer (a slide that has a ruler etched onto it) are lined up. It is then possible to calculate the length of the divisions on the eyepiece graticule.
• Uncertainty is the amount of error your measurements might have.
• The uncertainty value of a piece of measuring equipment is ± half the value of the smallest unit of precision.
• If you are combining measurements, you’ll need to combine their uncertainties:

  • The uncertainty in the pipette is half of 0.5cm3 (so 0.25cm3) 
  • The uncertainty in the cylinder is half of 1cm3 (so 0.5cm3) 
  • So the total uncertainty will be 0.25cm3 + 0.5cm3 = ± 0.75cm3 
• Percentage error= uncertainty/ reading x 100