diff --git a/dyesub-tool/src/svg/measure.rs b/dyesub-tool/src/svg/measure.rs
index f16b4b4..4a63dd0 100644
--- a/dyesub-tool/src/svg/measure.rs
+++ b/dyesub-tool/src/svg/measure.rs
@@ -5,6 +5,7 @@ use std::{
     ops::{Add, Div, Mul, Sub},
 };
 
+#[derive(Debug, Clone, Copy)]
 pub struct SVGMeasure {
     pub measure: f64,
     pub unit: SVGUnit,
@@ -14,6 +15,29 @@ impl SVGMeasure {
     pub fn new(measure: f64, unit: SVGUnit) -> Self {
         Self { measure, unit }
     }
+
+    fn to_user_units(&self) -> f64 {
+        self.measure * self.unit.to_user_units()
+    }
+
+    fn to_unit(&self, unit: SVGUnit) -> Self {
+        SVGMeasure {
+            measure: self.to_user_units() / unit.to_user_units(),
+            unit,
+        }
+    }
+}
+
+const EQ_TOLERANCE: f64 = 0.00001;
+
+impl PartialEq for SVGMeasure {
+    fn eq(&self, other: &Self) -> bool {
+        (self.to_user_units() - other.to_user_units()).abs() < EQ_TOLERANCE
+    }
+
+    fn ne(&self, other: &Self) -> bool {
+        (self.to_user_units() - other.to_user_units()).abs() > EQ_TOLERANCE
+    }
 }
 
 impl Display for SVGMeasure {
@@ -25,31 +49,35 @@ impl Display for SVGMeasure {
 impl Add for SVGMeasure {
     type Output = Self;
 
-    fn add(self, other: Self) -> Self {
-        SVGMeasure::new(self.measure + other.measure, self.unit)
+    fn add(mut self, other: Self) -> Self {
+        self.measure += other.to_unit(self.unit).measure;
+        self
     }
 }
 
 impl Sub for SVGMeasure {
     type Output = Self;
 
-    fn sub(self, other: Self) -> Self {
-        SVGMeasure::new(self.measure - other.measure, self.unit)
+    fn sub(mut self, other: Self) -> Self {
+        self.measure -= other.to_unit(self.unit).measure;
+        self
     }
 }
 
 impl Mul<f64> for SVGMeasure {
     type Output = Self;
 
-    fn mul(self, scalar: f64) -> Self {
-        SVGMeasure::new(self.measure * scalar, self.unit)
+    fn mul(mut self, scalar: f64) -> Self {
+        self.measure *= scalar;
+        self
     }
 }
 
 impl Div<f64> for SVGMeasure {
     type Output = Self;
 
-    fn div(self, scalar: f64) -> Self {
-        SVGMeasure::new(self.measure / scalar, self.unit)
+    fn div(mut self, scalar: f64) -> Self {
+        self.measure /= scalar;
+        self
     }
 }
diff --git a/dyesub-tool/src/svg/mod.rs b/dyesub-tool/src/svg/mod.rs
index 2c4d0fd..979adce 100644
--- a/dyesub-tool/src/svg/mod.rs
+++ b/dyesub-tool/src/svg/mod.rs
@@ -3,3 +3,6 @@ pub use unit::SVGUnit;
 
 mod measure;
 pub use measure::SVGMeasure;
+
+#[cfg(test)]
+mod tests;
\ No newline at end of file
diff --git a/dyesub-tool/src/svg/tests.rs b/dyesub-tool/src/svg/tests.rs
new file mode 100644
index 0000000..81ec57e
--- /dev/null
+++ b/dyesub-tool/src/svg/tests.rs
@@ -0,0 +1,46 @@
+use crate::svg::{SVGMeasure, SVGUnit};
+
+#[test]
+fn add() {
+    let m_10cm = SVGMeasure::new(10.0, SVGUnit::Centimeter);
+    let m_5mm = SVGMeasure::new(5.0, SVGUnit::Millimeter);
+    assert_eq!(m_10cm + m_5mm, SVGMeasure::new(10.5, SVGUnit::Centimeter));
+    assert_eq!(m_5mm + m_10cm, SVGMeasure::new(105.0, SVGUnit::Millimeter));
+}
+
+#[test]
+fn sub() {
+    let m_10cm = SVGMeasure::new(10.0, SVGUnit::Centimeter);
+    let m_5mm = SVGMeasure::new(5.0, SVGUnit::Millimeter);
+    assert_eq!(m_10cm - m_5mm, SVGMeasure::new(9.5, SVGUnit::Centimeter));
+    assert_eq!(m_5mm - m_10cm, SVGMeasure::new(-95.0, SVGUnit::Millimeter));
+}
+
+#[test]
+fn mul() {
+    let m_10cm = SVGMeasure::new(10.0, SVGUnit::Centimeter);
+    assert_eq!(m_10cm * 5.0, SVGMeasure::new(50.0, SVGUnit::Centimeter));
+}
+
+#[test]
+fn div() {
+    let m_10cm = SVGMeasure::new(10.0, SVGUnit::Centimeter);
+    assert_eq!(m_10cm / 5.0, SVGMeasure::new(2.0, SVGUnit::Centimeter));
+}
+
+#[test]
+fn eq() {
+    let m_1in = SVGMeasure::new(1.0, SVGUnit::Inch);
+    assert_eq!(m_1in, m_1in);
+    let m_1cm = SVGMeasure::new(1.0, SVGUnit::Centimeter);
+    let m_10mm = SVGMeasure::new(10.0, SVGUnit::Millimeter);
+    assert_eq!(m_1cm, m_10mm);
+}
+
+#[test]
+fn ne() {
+    // Testing negative difference, there should be absolute value in PartialEq impl
+    let a = SVGMeasure::new(1.0, SVGUnit::Pixel);
+    let b = SVGMeasure::new(10.0, SVGUnit::Pixel);
+    assert_ne!(a, b);
+}
\ No newline at end of file
diff --git a/dyesub-tool/src/svg/unit.rs b/dyesub-tool/src/svg/unit.rs
index da85208..9c67baf 100644
--- a/dyesub-tool/src/svg/unit.rs
+++ b/dyesub-tool/src/svg/unit.rs
@@ -1,6 +1,7 @@
 use std::fmt::{self, Display};
 
 /// https://oreillymedia.github.io/Using_SVG/guide/units.html
+#[derive(Clone, Copy, PartialEq, Eq, Debug)]
 pub enum SVGUnit {
     /// Pixel units, directly equivalent to SVG user units.
     Pixel,
@@ -14,22 +15,20 @@ pub enum SVGUnit {
     Point,
     // Picas.
     Pica,
-    /// Em units. Equivalent to the computed font-size in effect for an element.
-    Em,
-    /// Ex units. Equivalent to the height of a lower-case letter in the font (and font-size) in effect for an element. If the font doesn’t include lower-case letters, or doesn’t include the metadata about the ex-height, then 1ex = 0.5em.
-    Ex,
-    /// Character units. Equivalent to the width of the `0` (zero) character in the font and font-size in effect for an element.
-    Character,
-    /// Root-em units. The font size of the root element in the document, regardless of any settings for the current element.
-    Rem,
-    /// Viewport width units. 1% of the viewport width.
-    ViewportWidth,
-    /// Viewport height units. 1% of the viewport height.
-    ViewportHeight,
-    /// Viewport minimum units. 1% of the viewport width or height, whichever is smaller.
-    ViewportMinimum,
-    /// Viewport maximum units. 1% of the viewport width or height, whichever is larger.
-    ViewportMaximum,
+}
+
+impl SVGUnit {
+    pub fn to_user_units(&self) -> f64 {
+        use SVGUnit::*;
+        match self {
+            Pixel => 1.0,
+            Inch => 96.0,
+            Centimeter => 37.795,
+            Millimeter => 3.7795,
+            Point => 4.0 / 3.0, // 1.3333
+            Pica => 16.0,
+        }
+    }
 }
 
 impl Display for SVGUnit {
@@ -45,14 +44,6 @@ impl Display for SVGUnit {
                 Millimeter => "mm",
                 Point => "pt",
                 Pica => "pc",
-                Em => "em",
-                Ex => "ex",
-                Character => "ch",
-                Rem => "rem",
-                ViewportWidth => "vw",
-                ViewportHeight => "vh",
-                ViewportMinimum => "vmin",
-                ViewportMaximum => "vmax",
             }
         )
     }