diff --git a/src/gray_params.f90 b/src/gray_params.f90
index 5ea416b..0e721ff 100644
--- a/src/gray_params.f90
+++ b/src/gray_params.f90
@@ -93,7 +93,7 @@ module gray_params
     real(wp_), allocatable :: psin(:,:) ! Poloidal flux on a uniform grid
     real(wp_), allocatable :: psinr(:)  ! Poloidal flux
     real(wp_) :: psia                   ! Poloidal flux at edge - flux at magnetic axis
-    real(wp_) :: rvac                   ! Reference R₀ (B = B₀R₀ without the plasma)
+    real(wp_) :: rvac                   ! Reference R₀ (B = B₀R₀/R without the plasma)
     real(wp_) :: rax                    ! R of the magnetic axis
     real(wp_) :: zax                    ! Z of the magnetic axis
   end type