Fix reciprocal minor tick spacing; bump to 0.84

Minor ticks on 1/x scales were using linear value interpolation between
harmonically-spaced major ticks. Because 1/v is highly convex, equal value
steps near a large major-value (left side of the first interval) map to tiny
physical steps, piling all ticks against the left wall. At a 1:1000 ratio the
first four minor ticks land at 0%/0%/1%/2% of the interval.

Fix: interpolate in position space (uniform physical spacing) for all
reciprocal intervals, matching how major ticks are laid out (also equal
physical steps) and matching the already-correct ∞-first-interval handling.

Also documents 1/x scale and ∞ max in README.

README.md

@@ -65,8 +65,9 @@ Calculated numbers are rendered in fixed-point notation at 4 significant figures
 | Linear | Evenly spaced | Uniform | None |
 | √ | Quadratic (0, 1, 4, 9 … × max) — compresses low values | Crowded toward the low end of each interval | Min ≥ 0 |
 | Log | Geometric (min × r⁰, r¹, r² …) — each interval spans the same ratio | Crowded toward the high end of each interval | Min and Max > 0 |
+| 1/x | Harmonic (values decrease left → right, e.g. ∞, 10, 5, 2, 1) — compresses high values | Uniform (in position space, i.e. proportional to 1/v) | Min and Max > 0; Max may be ∞ |
 
-The √ mapping is typical for AC RMS current and power meters, where needle deflection is proportional to the square of the measured quantity.
+The √ mapping is typical for AC RMS current and power meters, where needle deflection is proportional to the square of the measured quantity. The 1/x mapping is used for ohms/resistance scales, where values decrease from left (high resistance / ∞) to right (low resistance).
 
 ### Unit markup
 

k8s/deployment.yaml

@@ -15,7 +15,7 @@ spec:
     spec:
       containers:
         - name: m1730-generator
-          image: git.baumann.gr/adebaumann/m1730-generator:0.83
+          image: git.baumann.gr/adebaumann/m1730-generator:0.84
           imagePullPolicy: Always
           ports:
             - containerPort: 5000

web/app.py

@@ -8,7 +8,7 @@ from fontTools.pens.svgPathPen import SVGPathPen
 
 app = Flask(__name__)
 
-VERSION = "0.83"
+VERSION = "0.84"
 
 _LOGO_PATH = pathlib.Path(__file__).parent / 'static' / 'logo.png'
 _LOGO_B64 = base64.b64encode(_LOGO_PATH.read_bytes()).decode()
@@ -487,9 +487,10 @@ def generate_svg(unit, min_val, max_val, range_label, big_ticks, small_ticks, la
             for j in range(1, small_ticks + 1):
                 if scale_type == 'sqrt':
                     x = big_xs[i] + (j / sub) ** 2 * (big_xs[i + 1] - big_xs[i])
-                elif math.isinf(big_vals[i]):
-                    # First interval with ∞ at the left: interpolate in position space
-                    # (linear value interpolation is undefined from ∞).
+                elif scale_type == 'reciprocal' or math.isinf(big_vals[i]):
+                    # Reciprocal: interpolate in position space (= linear in 1/v).
+                    # Linear value interpolation would map huge early value ranges
+                    # through 1/v and pile all ticks against the left wall.
                     x = big_xs[i] + (j / sub) * (big_xs[i + 1] - big_xs[i])
                 else:
                     v = big_vals[i] + j * (big_vals[i + 1] - big_vals[i]) / sub