From 0e9a7e9508a5c7c0107aa2475b7e6770e25857c5 Mon Sep 17 00:00:00 2001
From: Sam Anthony <sam@samanthony.xyz>
Date: Thu, 25 Sep 2025 11:03:52 -0400
Subject: vacuum permettivity constant

---
 const.go    | 7 +++++++
 doc/const.1 | 4 ++++
 2 files changed, 11 insertions(+)

diff --git a/const.go b/const.go
index 3808e82..0aa5a37 100644
--- a/const.go
+++ b/const.go
@@ -2,12 +2,19 @@ package main
 
 import "math"
 
+const (
+	// Vacuum permettivity [C²/(N·m²)]
+	e0 = 8.8541878188e-12
+)
+
 func parseConstant(s string) (float64, error) {
 	switch s {
 	case "pi":
 		return math.Pi, nil
 	case "e":
 		return math.E, nil
+	case "e0":
+		return e0, nil
 	}
 	return 0, InvalidConstantErr{s}
 }
diff --git a/doc/const.1 b/doc/const.1
index a4eb3b6..9c32108 100644
--- a/doc/const.1
+++ b/doc/const.1
@@ -7,3 +7,7 @@ Archimedes’ constant (π).
 .TP
 .B e
 Euler’s number (e).
+.
+.TP
+.B e0
+Vacuum permettivity (ε₀)
-- 
cgit v1.2.3