diff --git a/src/devices/accessories/headset/specification.jd b/src/devices/accessories/headset/specification.jd
index 2a3435d..08eaf65 100644
--- a/src/devices/accessories/headset/specification.jd
+++ b/src/devices/accessories/headset/specification.jd
@@ -193,7 +193,7 @@
 based on the microphone capsule resistance (Rmic) and the equivalent impedance
 values (ReqA-ReqD). Use the following formula:</p>
 
-<p><em>Rn=(Rmic*ReqN) / (ReqN-Rmic)</em></p>
+<p><em>Rn=(Rmic*ReqN) / (Rmic+ReqN)</em></p>
 
 <p>Where R<em>n</em> is the actual resistance of a button, Req<em>N</em> is the
 equivalent impedance value of that button (provided), and Rmic is the