diff --git a/beamform_image.ipynb b/beamform_image.ipynb
index 71306c7..951ce8d 100644
--- a/beamform_image.ipynb
+++ b/beamform_image.ipynb
@@ -926,9 +926,10 @@
         "\n",
         "Instructions: \n",
         "- Use a ruler and measure the full width (start and end points) of your reflection target in the lateral and axial directions. \n",
-        "- One full width is equal to approximately 6 standard deviations (sigma).\n",
+        "- One full width is equals approximately 6 standard deviations (± 3$\\sigma$ = 99.73%).\n",
         "- Divide the full width by 6 to get the approximate value of one sigma.\n",
-        "- Calculate the full width at half maximum (FWHM) using a Gaussian distribution: FWHM = 2*sqrt(2 *ln2) * sigma\n"
+        "- Calculate the full width at half maximum (FWHM) using a Gaussian distribution: $FWHM = 2 \\sqrt{2 ln2} * \\sigma$\n",
+        "- You can do the calculation in <a href=\"https://www.wolframalpha.com/\">https://www.wolframalpha.com/</a>"
       ],
       "metadata": {
         "id": "hvN5S63KU8lh"