Blackwell Radiation Treatment Time Calculator for use with Theratron model B cobalt 60 radiotherapy machine, used to assess appropriate length of patient exposure to radiation during cancer therapy treatment, made by Abbot Brown, Beaminster, United Kingdom, 1955-75.

Radiation therapy or radiotherapy is used to kill cancerous cells in the body and prevent them spreading. However, too much radiation is dangerous as it can affect surrounding healthy cells. This calculator would have been used to determine exactly how long the treatment should last.

Carried out in specialised hospital units, radiotherapy treatments are spread out over days and weeks to allow healthy cells to recover. The calculator was made by Abbot Brown, a printer based in Dorset, England.