diff --git a/src/new/optical_tools/FT_FP_cavity_power.m b/src/new/optical_tools/FT_FP_cavity_power.m
index b70ba83617b45321fb592e713a05ba51a920d1d2..2a9176cecf60b784b8da275ad36429021a56a75c 100644
--- a/src/new/optical_tools/FT_FP_cavity_power.m
+++ b/src/new/optical_tools/FT_FP_cavity_power.m
@@ -1,5 +1,5 @@
 %--------------------------------------------------------------------------
-% function [Lrt] = FT_FP_cavity_power(Pin,Lrt,lambda,L,T1,R1,R2)
+% function [Ploss,P0] = FT_FP_cavity_power(Pin,Lrt,lambda,L,T1,R1,R2)
 %
 % A function for Matlab which calculates the power circulating in a lossy
 % Fabry-Perot cavity.  N.B. the circulating power is calculated just after
@@ -32,7 +32,7 @@ function [Ploss,P0] = FT_FP_cavity_power(Pin,Lrt,lambda,L,T1,R1,R2)
     P0 = Pin * T1/(1+R1*R2-2*r1*r2);
 
     % Calculate power in lossy cavity
-    Ploss = P0/(1+Lrt/T1)^2;
+    Ploss = P0./(1+Lrt/T1).^2;
     
 end