Scale unit label font size to fit left panel for multi-character strings

web/app.py

@@ -26,6 +26,16 @@ BIG_H = 5.0895    # major tick height
 SMALL_H = 2.6683  # minor tick height
 
 
+_UNIT_AREA_WIDTH = 18.445  # canvas mm available for the unit label
+_UNIT_SCALE_X = 0.96486402
+_UNIT_CHAR_EM = 0.65       # approximate advance-width ratio for GOST typ A
+
+
+def _unit_font_size(unit: str) -> float:
+    n = max(1, len(unit))
+    return min(18.7981, _UNIT_AREA_WIDTH / (n * _UNIT_SCALE_X * _UNIT_CHAR_EM))
+
+
 def _fmt(v: float) -> str:
     if v == int(v):
         return str(int(v))
@@ -54,7 +64,7 @@ def generate_svg(unit, min_val, max_val, range_label, big_ticks, small_ticks, la
         ' M 58.443978,107.54692 H 183.64409 v 6.19963 H 58.443978 Z" />',
 
         # Unit label (large letter in left panel)
-        f'    <text style="font-size:18.7981px;font-family:\'ГОСТ тип А\',monospace;fill:#1a1a1a"'
+        f'    <text style="font-size:{_unit_font_size(unit):.4f}px;font-family:\'ГОСТ тип А\',monospace;fill:#1a1a1a"'
         f' x="41.455711" y="109.03796"'
         f' transform="scale(0.96486402,1.0364155)">{escape(unit)}</text>',