An overhead perspective captures an open textbook resting on a light brown wooden surface in Varna, Bulgaria

An overhead perspective captures an open textbook resting on a light brown wooden surface in Varna, Bulgaria. The textbook, displaying text in Bulgarian, features mathematical equations, a table labeled "Таблица 1" containing numerical data, and a black and white photographic illustration of a tall, cylindrical scientific apparatus, identified as likely an Oberbeck pendulum, on the right page. A section heading "Задача 1. Определяне на константата на махалото на Обербек" is visible. A human hand is partially visible in the top-left corner, resting near the edge of the left page. A gray graphite pencil with a black eraser tip is positioned horizontally on the wooden surface near the top-right corner of the open book. The page number "18" is printed at the bottom center of the visible spread.