Add reciprocal (1/x) scale mapping

web/app.py

@@ -8,7 +8,7 @@ from fontTools.pens.svgPathPen import SVGPathPen
 
 app = Flask(__name__)
 
-VERSION = "0.81"
+VERSION = "0.82"
 
 _LOGO_PATH = pathlib.Path(__file__).parent / 'static' / 'logo.png'
 _LOGO_B64 = base64.b64encode(_LOGO_PATH.read_bytes()).decode()
@@ -362,6 +362,19 @@ def generate_svg(unit, min_val, max_val, range_label, big_ticks, small_ticks, la
         def major_value(i):
             return min_val + span * (i / big_ticks) ** 2
 
+    elif scale_type == 'reciprocal':
+        if min_val <= 0 or max_val <= 0:
+            raise ValueError("Reciprocal scale requires min and max values greater than 0.")
+        if max_val <= min_val:
+            raise ValueError("Reciprocal scale requires max value greater than min.")
+        k = 1.0 / min_val - 1.0 / max_val   # always positive
+
+        def value_to_x(v):
+            return ZERO_X + SCALE_LEN * (1.0 / v - 1.0 / max_val) / k
+
+        def major_value(i):
+            return 1.0 / (1.0 / max_val + i / big_ticks * k)
+
     else:
         span = max_val - min_val