Checking Postgres Streaming replication delay

Hi guys,

I'm using this query to measure the delay between a Master and a Streaming
Replication Slave server, using PostgreSQL 9.2.

SELECT
> pg_last_xlog_receive_location() receive,
> pg_last_xlog_replay_location() replay,
> (
> extract(epoch FROM now()) -
> extract(epoch FROM pg_last_xact_replay_timestamp())
> )::int lag;

In your opinion, is that right?

Cheers

Patrick