This page illustrates a comparison of the fine focus mechanism of the earliest of the famous Powell & Lealand first class models from the first(left) and second(right) year of production. The earlier model uses a sprung wedge to move the long lever, whereas the second model uses a L-shaped piece; this form of revised side fine adjustment has been seen in other examples of P & L microscopes from the same time period. The fine adjustment knob was moved to the top of the arm starting in 1848, but both the side fine adjustment and the top fine adjustments are found in models dated 1848 and 1849. After that, starting in 1850, all the dated P & L microscopes have the fine adjustment on the top of the arm.*

Looking at other examples of P &L microscopes other than the model we are discussing here, we note that in Quekett's Treatice of 1848, where the side fine adjustment is pictured on the model shown here, a top fine adjustment is at the same time shown on the number 4 portable model. A persual of a database of most known examples does not show an extant example of the P & L portable from before 1850, though according to Turner in The Great Age of the Microscope the portable was introduced in 1847.

*Zeligs,Joseph: personal communication based on a database of known P & L examples. Only the top of the arm location was used from 1850 onward.