Your value of 530 with no current looks out of tolerance to me. The offset voltage at zero current and +5V supply is supposed to be +/-5mV typical at 25C, and you are reading (530 - 512)/1024 * 5V = 88mV.
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Do you have a 0.1uF decoupling capacitor between Vcc and ground of the device, as specified in the data sheet?
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Are you powering the Arduino from the USB port or from an external supply? A computer USB port doesn't the most stable source of power.
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Are you certain that you are reading from the correct analog input pin?