Updated README. Fixed tests for older OTP versions

README.md

@@ -654,9 +654,10 @@ The MF called should take no arguments and should return a value that can be be
 
 This metadata is also persistent across processes.
  
-**IMPORTANT**: Since you can calling functions, be aware that using these 
-could have an impact on your logging performance depending on what the call
-will need to do.
+**IMPORTANT**: Since this feature relies on function calls injected at the
+point where a log message is emitted, your logging performance (ops/sec)
+will be impacted by what the functions you call do and how much latency they
+may introduce.
 
 
 Setting the truncation limit at compile-time

test/lager_test_function_transform.erl

@@ -44,7 +44,12 @@ transform_static() ->
   static_result.
 
 transform_dynamic() ->
-  erlang:monotonic_time().
+  case lager_util:otp_version() >= 18 of
+    true ->
+      erlang:monotonic_time()
+    false ->
+      erlang:now()
+  end.
 
 not_running_test() ->
   ?assertEqual({error, lager_not_running}, lager:log(info, self(), "not running")).