From cf844d007be74248462378207d90ce6475ed9ce9 Mon Sep 17 00:00:00 2001
From: "Adrian A. Baumann" <ade@adebaumann.com>
Date: Tue, 14 Jul 2026 23:25:01 +0200
Subject: [PATCH] Add reciprocal (1/x) scale mapping

---
 k8s/deployment.yaml      |  2 +-
 web/app.py               | 15 ++++++++++++++-
 web/templates/index.html |  5 +++++
 3 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/k8s/deployment.yaml b/k8s/deployment.yaml
index 89ac4ae..c4f422a 100644
--- a/k8s/deployment.yaml
+++ b/k8s/deployment.yaml
@@ -15,7 +15,7 @@ spec:
     spec:
       containers:
         - name: m1730-generator
-          image: git.baumann.gr/adebaumann/m1730-generator:0.81
+          image: git.baumann.gr/adebaumann/m1730-generator:0.82
           imagePullPolicy: Always
           ports:
             - containerPort: 5000
diff --git a/web/app.py b/web/app.py
index e2be9a4..d36decc 100644
--- a/web/app.py
+++ b/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
 
diff --git a/web/templates/index.html b/web/templates/index.html
index 23cdecd..5199478 100644
--- a/web/templates/index.html
+++ b/web/templates/index.html
@@ -322,6 +322,8 @@
                 title="Square-root scale — ticks crowd at the low end; used for RMS current/power meters. Min must be ≥ 0">√</button>
               <button type="button" class="mode-btn" data-scale="log"
                 title="Values spaced logarithmically — requires min and max greater than 0">Log</button>
+              <button type="button" class="mode-btn" data-scale="reciprocal"
+                title="Reciprocal (1/x) scale — values decrease left to right; used for resistance (ohms) scales. Min and Max must be greater than 0, Max greater than Min">1/x</button>
             </div>
           </div>
           <div class="field">
@@ -442,6 +444,9 @@
               if (!(parseFloat(maxInput.value) > 0)) maxInput.value = '100';
             } else if (btn.dataset.scale === 'sqrt') {
               if (parseFloat(minInput.value) < 0) minInput.value = '0';
+            } else if (btn.dataset.scale === 'reciprocal') {
+              if (!(parseFloat(minInput.value) > 0)) minInput.value = '1';
+              if (!(parseFloat(maxInput.value) > parseFloat(minInput.value))) maxInput.value = String(parseFloat(minInput.value) * 10);
             }
           }
           doGenerate();