In years gone by, I plunked alot. Instead of lead we used smaller Railroad spikes tied on with cotton string at Tanner . I have not done that in years. No matter what you use for weight. You normally lose it.
Mine varies. At the time the reading was taken , it was foggy. Also, thermometer is about 20 feet from a large pond that did not freeze over. Look at my last reading, humidity was lower.