diff --git a/PCR_formula.R b/PCR_formula.R
index cfa4b31..0dbd415 100644
--- a/PCR_formula.R
+++ b/PCR_formula.R
@@ -1,7 +1,18 @@
+#### DESCRIPTION:
 # These functions use the PCR equation to calculate
 # the number of PCR products after N cycles starting
 # from x molecules of the template.
 
+
+#### HOW TO USE:
+# source('https://github.com/dchakro/shared_Rscripts/raw/master/PCR_formula.R')
+# prettyNum(PCRamp(1,30),big.mark = " ")
+# 
+# print(paste("Cycle",1:30,"=",
+#             prettyNum(PCRamp.steps(1,30),
+#                       big.mark = " ")),
+#       width = 40)
+
 PCRamp = function(x, n){
   # calculates number of amplicons starting from x initial DNA molecules in n cycles.
   x*((2^n)-2*n)