I was trying to use an online sha-256 calculator to verify blocks, but I have had no luck. I was just stringing together the "header" and applying the sha-256 algorithm twice. Then I noticed that I get different results to "hello" than is displayed on the wiki. It shows two rounds of the hash algorithm. I get a match for the first round, but not on the second. Any idea what is going on here? Thanks

https://en.bitcoin.it/wiki/Protocol_specification