From 1f50c359dc685e5803ac57f53a3caa9c50dc1b68 Mon Sep 17 00:00:00 2001
From: Petar Petrov <MindFreeze@users.noreply.github.com>
Date: Tue, 25 Feb 2025 13:00:33 +0200
Subject: [PATCH] Fix history Y axis with tiny values (#24342)

* Fix history Y axis with tiny values

* set min fractions to 2

* handle negative values
---
 src/components/chart/state-history-chart-line.ts | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/src/components/chart/state-history-chart-line.ts b/src/components/chart/state-history-chart-line.ts
index e2953937d9..79d47fb90d 100644
--- a/src/components/chart/state-history-chart-line.ts
+++ b/src/components/chart/state-history-chart-line.ts
@@ -259,7 +259,21 @@ export class StateHistoryChartLine extends LitElement {
           axisLabel: {
             margin: 5,
             formatter: (value: number) => {
-              const label = formatNumber(value, this.hass.locale);
+              const formatOptions =
+                value >= 1 || value <= -1
+                  ? undefined
+                  : {
+                      // show the first significant digit for tiny values
+                      maximumFractionDigits: Math.max(
+                        2,
+                        -Math.floor(Math.log10(Math.abs(value % 1 || 1)))
+                      ),
+                    };
+              const label = formatNumber(
+                value,
+                this.hass.locale,
+                formatOptions
+              );
               const width = measureTextWidth(label, 12) + 5;
               if (width > this._yWidth) {
                 this._yWidth = width;