nce last difficulty change.
2. height      (numeric, optional, default=-1) To estimate at the time of the given height.

Result:
x             (numeric) Hashes per second estimated

Examples:
> bitcoin-cli getnetworkhashps 
> curl --user myusername --data-binary '{"jsonrpc": "1.0", "id":"curltest", "method": "getnetworkhashps", "params": [] }' -H 'content-type: text/plain;' http://127.0.0.1:8332/


