diff --git a/src/main.rs b/src/main.rs
index 249caf6..7f26000 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -147,7 +147,7 @@ fn main() -> ! {
                                             let dac_i = dac_feedback / Ohms(5.0);
 
                                             let itec = channels.read_itec(channel);
-                                            let tec_i = Amps((itec.0 - 1.5) / 8.0);
+                                            let tec_i = (itec - Volts(1.5)) / Ohms(0.4);
 
                                             let state = channels.channel_state(channel);
                                             let _ = writeln!(
diff --git a/src/units.rs b/src/units.rs
index 86e55b8..1bf8ea2 100644
--- a/src/units.rs
+++ b/src/units.rs
@@ -1,10 +1,29 @@
 use core::{
     fmt,
-    ops::Div,
+    ops::{Add, Div, Sub},
 };
 
+macro_rules! impl_add_sub {
+    ($Type: ident) => {
+        impl Add<$Type> for $Type {
+            type Output = $Type;
+            fn add(self, rhs: $Type) -> $Type {
+                $Type(self.0 + rhs.0)
+            }
+        }
+
+        impl Sub<$Type> for $Type {
+            type Output = $Type;
+            fn sub(self, rhs: $Type) -> $Type {
+                $Type(self.0 - rhs.0)
+            }
+        }
+    }
+}
+
 #[derive(Debug, Clone, Copy, PartialEq, PartialOrd)]
 pub struct Volts(pub f64);
+impl_add_sub!(Volts);
 
 impl fmt::Display for Volts {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
@@ -21,6 +40,7 @@ impl Div<Ohms> for Volts {
 
 #[derive(Debug, Clone, Copy, PartialEq, PartialOrd)]
 pub struct Amps(pub f64);
+impl_add_sub!(Amps);
 
 impl fmt::Display for Amps {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
@@ -29,6 +49,7 @@ impl fmt::Display for Amps {
 }
 #[derive(Debug, Clone, Copy, PartialEq, PartialOrd)]
 pub struct Ohms(pub f64);
+impl_add_sub!(Ohms);
 
 impl fmt::Display for Ohms {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {