A G Thornton slide rule. Manchester UK, makers of Surveying and Scientific equipment from 1900. Established 1878, this is a Thornton model 121 slide rule 10 inch closed frame, with slide rule books on reverse, for use in evaluating engines, catalogued in 1916 as Thornton's improved slide rule. As used by Atomic Energy UK. It has the previous engineer's name on it, P Gardiner (in the well) there is a small 50 incuse mark on the back which is the date letter for 1950. Made in England, they were previously made in Germany by Nestler for Thornton's prior to WW1. Please study the photos, you will see a very nice item.UK sales only please.