I think Geof's stereo will have the same serial number on both barrels - because:

- I own no. 302 which is not the 302 shown in the photo of Corrado's book!

- My set has both 38 and 38 (S) as extra lenses. I guess that one "stack" of Waterhouse Stops has the additional (S), whilst the other was without. I cannot think think of any reason whay, other than it would be easier to check all appropriate sizes in both stacks.

- The stereo set which was split into two in the 19th century (perhaps even by Darlot if sales of ready-made stereo sets was poor), contained one misplaced stop in each of the halves!

Note that there is an additional section on the Darlot Universal on pages 356 - 358, which covers usage very well.