when mixing alcohol drink, what is the different between one part and one count? How do I pour 1 part?

Question by flash_2000: when mixing alcohol drink, what is the different between one part and one count? How do I pour 1 part?
I’m learning to bartend but confuse with the measurement in alcohol mix. Some recipe use “count” as measurement and some use “part”, i wonder how to measure part. & can anyone recommend a good bartender hand book that i can carry to work?

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