Perrygraf Naval underwater Convergence zone range slide chart 1973 USA

Interesting slide chart by Perrygraf, called the Convergence Zone Range slide rule. Made for the Naval underwater system center (part of the USA Navy) in 1973. When you need to know about underwater sound propagation, you need to know if they sea you are studying has a convergence zone and if so, what that zone would look like in terms of range and depth. This slide rule charts helps with that…fortunately it comes with the original paper wrapper that doubles as a manual and case. It also contains instructions of all the corrections that need to be take into account. It is a thrilling piece of calculating equipment with a very distinctive field of use. It measures ca. 20 cm or ca. 8 inches wide. Check the attached video on how to work your vintage man tool : slide rule operation instructions!