How Calculate GPU Cracking Time

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Speed was lower because you cracked the password immediately, didn't get a chance to do any work. Moreover, as was already mentioned, you need to add an amplifier to gain any acceleration.

What is that mean amplifier?
also am im doing the right command to check my PC to see how many passwords he can try in a word list?
im using

Code:

hashcat64 -m0 "my hash" wordlist.txt --speed-only

or should i use something else