Clark

 
"Any pigmented lesion that can be covered by the unused eraser of an ordinary yellow pencil is likely to be benign or a curable form of malignant melanoma (except for the uncommon nodular melanoma). Concentrate on those lesions larger than the eraser (7 mm)."
 
Clark WH Jr. Clinical diagnosis of cutaneous malignant melanoma. JAMA 1976;236:484–5.
 

Brief critique

 
The idea that a "pigmented lesion" less than 7 mm in diameter is "benign or a curable form of malignant melanoma" is specious. Nearly always, primary cutaneous melanomas begin as a macule that is much smaller than 7 mm in diameter. Moreover, melanomas, except for those rare examples in prepubescent children, do not evolve in a fashion analogous to Athena springing from the brow of Zeus; they begin as a tiny macule that grows remarkably slowly. Clinicians should not concentrate on pigmented lesions larger than 7 mm, but on ones that are flat of any size, no matter how small or how large. When a melanoma is flat and without signs of regression, it is curable by simple excision.