In this photo of a portion of one of our used barograph charts, you can see the change of air pressure over time. Each chart is capable of recording a continuous ink line of 7 days. The bowed red vertical lines represent hours of the day in 2-hour increments. The red horizontal lines represent air pressure in milibars in 1 milibar increments. The blue ink line was traced by the pen arm. Time on this chart moves from left to right. At both the top and bottom of the chart are the days of the week, the limits of those days are denoted by brackets from midnight-to-midnight. What you see here shows a portion of a seven-day chart from midnight Monday through almost 5:00 am Friday morning. Before the times of automated stations, these charts were observers’ only way to record continuous air pressure readings. Charts were replaced every week to avoid having the pen arm trace overtop of the previous week’s record.
~ Steve Woodruff and Devin Lussier