The use of transparent drawing film must have been a huge help in 
digging stratified sites because it allowed the multiple overlay of 
plans without the distortion and other problems  of tracing paper- a key 
aspect of  open area excavation techniques on stratified sites from hill 
forts and monasteries to urban tenements. I asked a few colleagues  this 
morning and we couldn't fix its introduction into archaeological use 
(?1960s) but remembered graph paper still being use in the early 70s on 
some sites and drawing film on others presumably with more money.


paul