Sorry ... its  

 W = ρ g &nabla 
 where;: 
 :W = weight or displacement 
 :ρ = density 
 :g = gravity 
 :∇ = volume 

 This means that if ∇ is in ft3, displacement (δ) is: 

 δ(in long tons) = ∇ / 35.0 
 δ(in pounds) = ∇ x 64 

 I have changed the article appropriately. 

 Thanks,