Factual error: A number of the cars have number plates in which the numbers precede the letters, whereas at the time the letters came first.
Factual error: Eternity Ring is set in 1946. Samantha was accused of spying because she was seen with a man outside The Old Vic. She admits seeing a play there but not the play alleged (Henry V instead of The Cherry Orchard). The Old Vic was bombed in the Blitz and was closed from 1941 to 1950.
Factual error: Foyle is disembarking from a trans-Atlantic voyage from a ship which, in long shot, is painted in Union-Castle line colours. This line served African ports, not the USA. Their ships had lavender-coloured hulls from the mid-50s.
Factual error: The American flag shown has 50 stars, not the 48 stars that were on the flag at that time.
Factual error: SS officers did not carry a unit identification tattoo on the forearm, as implied in this episode. Most (but not all) carried a small, black, blood group tattoo under the armpit.
Factual error: Sunflowers are not grown in the North of France. They're grown primarily in Provence and Poitou.
Answer: They are using the accepted names of the bombs. During World War 2 the Germans used the metric system and produced bombs ranging from 50kg to 2500kg. Referring to the weight of the bombs in pounds (or fractions of tons) risked confusing the situation and would require someone to understand how to convert from imperial measures to metric, not an easy thing to do when under stress.