Final answer:
Using a light microscope with an oil immersion lens, platelet estimates on a differential blood smear are obtained by averaging platelet counts over several fields after initially assessing red blood cells and platelets then counting white blood cell types.
Step-by-step explanation:
Platelet estimates are performed by counting the number of platelets seen on the differential blood smear as averaged over several oil immersion fields. After staining with Wright-Giemsa stain, the smear is observed under a light microscope at high magnification using an oil immersion objective lens. During this process, an initial scan is carried out to assess the appearance of red blood cells and platelets, followed by a detailed analysis where each white blood cell type is identified and counted up to 100 cells. This method helps determine the number of platelets and analyze various cell populations present in the blood.