Plastic sextants are often disparaged for lack of inherent accuracy and vulnerability to the effects of the sun, but these criticisms are typically overstated. While it is true they are not as accurate as metal sextants and they are indeed more sensitive to the sun than metal sextants are, plastic sextants can with special care still be used quite successfully for practical navigation at sea, and they provide a less-expensive alternative to metal sextants, for both new navigators or seasoned mariners looking for a back up to GPS. Plastic sextants are even preferable over metal ones for most sextant-piloting applications.
This book explains how to get the best results from these instruments, including step by step instructions for the sight taking, as well as numerical comparisons with metal sextants.
Will also improve your sights and skills with metal sextants
The focus of the book is on plastic sextants, because they present the biggest challenges, but if you master the use of them, you will be even much better with a metal sextant in your hand. In short, the sight taking and analysis procedures covered are the best way to do all sights, regardless of sextant style, it is just more crucial that we follow these procedures when using plastic sextants.
This new edition now includes a detailed discussion of sextant piloting on inland and coastal waters, which is not covered in many texts these days.
PB 100 pages