diff --git a/basicmath.cpp b/basicmath.cpp
index 1c4641312abc32c6d6a5e217b1b1244898d17c18..74cfcc97d236ed075d18d054737f55e270a5e7ff 100644
--- a/basicmath.cpp
+++ b/basicmath.cpp
@@ -411,3 +411,10 @@ std::vector<eis::DataPoint> eis::fitToFrequencies(std::vector<fvalue> omegas, co
 
 	return out;
 }
+
+void difference(std::vector<eis::DataPoint>& a, const std::vector<eis::DataPoint>& b)
+{
+	assert(a.size() == b.size());
+	for(size_t i = 0; i < a.size(); ++i)
+		a[i] = a[i] - b[i];
+}
diff --git a/eisgenerator/basicmath.h b/eisgenerator/basicmath.h
index d5571800d93782e3f60e0a547584acc123da911a..4d9d7ffa2c9c596e401d0a698f837407f4e181d2 100644
--- a/eisgenerator/basicmath.h
+++ b/eisgenerator/basicmath.h
@@ -89,6 +89,17 @@ namespace eis
 	*/
 	std::complex<fvalue> median(const std::vector<eis::DataPoint>& data);
 
+
+	/**
+	* @brief Calculates the difference between two spectra.
+	*
+	* this function calculates an element wise a = a-b and ingores omega
+	*
+	* @param a The first operand, where b is subtracted
+	* @param b The second operand that is subtracted from the first, must be the same size as a
+	*/
+	void difference(std::vector<eis::DataPoint>& a, const std::vector<eis::DataPoint>& b);
+
 	/**
 	* @brief Resamples the data to the given amount of points.
 	*