diff --git a/src/parse_clock.jl b/src/parse_clock.jl
index a8a5955..b165bf0 100644
--- a/src/parse_clock.jl
+++ b/src/parse_clock.jl
@@ -28,14 +28,14 @@ function get_skew(file::T) where {T <: AbstractString}
         if high > 0
             @debug "Unexpected first line" file
             return missing
-        elseif high > 500
+        elseif high >= 500
             return time
         end
     end
 
     time_and_counts = Iterators.map(_parse_line, lines)
     for (time, high) in time_and_counts
-        if high > 500
+        if high >= 500
             return time
         end
     end
@@ -43,4 +43,44 @@ function get_skew(file::T) where {T <: AbstractString}
     return missing
 end
 
+"""
+    search_oscillation(file::T) where {T <: AbstractString}
+
+Search oscillation (two or more rise up) for clock measurement file.
+"""
+function count_riseup(file::T) where {T <: AbstractString}
+    lines = Iterators.Stateful(eachline(file))
+
+    rising_count = 0
+    first_line = popfirst!(lines)
+    is_high = let
+        time, high = _parse_line(first_line)
+        high >= 500
+    end
+
+    time_and_counts = Iterators.map(_parse_line, lines)
+    for (time, high) in time_and_counts
+        if !is_high && high >= 500
+            is_high = true
+            rising_count += 1
+        elseif is_high && high < 500
+            is_high = false
+        end
+    end
+
+    return rising_count
+
+    # lines = eachline(file)
+    # time_and_counts = Iterators.map(_parse_line, lines)
+    # is_high = Iterators.map(time_and_counts) do (time, counts)
+    #     counts >= 500
+    # end
+    # edges = Iterators.map(accumulate((p, n) -> (n, !p[1] & n), is_high, init = (false, false))) do x
+    #     _prev, edge = x
+    #     edge
+    # end
+    #
+    # return sum(edges)
+end
+
 end # module ClockParser