new file mode 100644
--- /dev/null
+++ b/libtides.pl
@@ -0,0 +1,44 @@
+#======================================================================
+#                    L I B T I D E S . P L 
+#                    doc: Thu Aug 24 21:37:14 2006
+#                    dlm: Thu Apr 26 10:22:53 2012
+#                    (c) 2006 A.M. Thurnherr
+#                    uE-Info: 17 0 NIL 0 0 72 2 2 4 NIL ofnI
+#======================================================================
+
+# tidal calculations
+
+# HISTORY:
+#   Aug 24, 2006: - created during GRAVILUCK
+#   Jan 22, 2008: - renamed M2() to M2_bias()
+#                 - added M2_phase()
+#   Apr 26, 2012: - added K1 & M2 tidal frequencies
+
+#----------------------------------------------------------------------
+# tidal frequencies
+#   - taken from thesis Makefile
+#   - according to my memory, the values are from Apel's book
+#----------------------------------------------------------------------
+
+$M2 = 24/1.9322;
+$K1 = 24/1.0027;
+
+#----------------------------------------------------------------------
+# given t0, a decimal day at the beginning of "flood", return a scale
+# between -1 and 1 that can be multiplied with the max tidal flow amplitude
+# to estimate tidal velocity at time t. 
+#----------------------------------------------------------------------
+
+sub M2_bias(@)
+{
+	my($t0,$t) = &antsFunUsage(2,'ff','time-origin, time',@_);
+	return sin(2*3.14159265358979 * ($t-$t0) / ($M2/24));
+}
+
+sub M2_phase(@)
+{
+	my($t0,$t) = &antsFunUsage(2,'ff','time-origin, time',@_);
+	return round(360 * frac(($t-$t0) / ($M2/24)));
+}
+
+1;