Tumours may be described as benign or malignant. Malignant tumours can lead to greater complications for the person with the tumour. Early identification of tumours, particularly malignant tumours, is important for effective treatment. Benign tumour cells and malignant tumour cells can look similar when viewed using a light microscope. Some scientists wanted to develop a diagnostic test to identify tumour cells as benign or malignant. The scientists investigated whether the diameter of the cell nucleus could be used to identify the type of tumour cell as benign or malignant. The scientists used a light microscope with a calibrated eyepiece graticule to measure the diameter of the nuclei of stained tumour cells. [Figure 2.1] shows a photomicrograph of stained tumour cells viewed using a light microscope. An eyepiece graticule was placed across the nucleus of one of the tumour cells. The calibration of the eyepiece graticule scale is: one eyepiece graticule division = 320nm