Note: Hilger & Watts produced several theodolite models (e.g., TM 1A, TM 6, 20-second, 1-second). The following is a general guide applicable to their classic 6-inch (150mm) glass circle theodolites, which are the most common in collections and field use today.

This is the most unique part of Hilger & Watts instruments. The manual describes a :

Physical copies can be difficult to find and are often prone to "field wear" (stains and torn pages).

A very specific request!