A photograph of an open exercise notebook lying on a yellow surface. The left page holds hand-drawn technical diagrams of an economiser with numbered parts and a dead weight safety valve with labelled weights, valve, valve seat and discharging casing. The right page is handwritten in blue ink with headings for Economiser and Result, describing feed water preheated by flue gases and a studied simple vertical boiler, with a circled number 23 at the bottom. No people are visible.