ADC and voltage regulator

hi,

i'm reading temperaure tmp36 module.

i connect module analogue input pin, read value, convert voltage , convert temperature - shown.....

code: [select]

        temp1 = analogread(temp1pin);          // input value (0-1013) analog pin
        temp1 = map(temp1,0,1023,0,regvolt);   // convert millivolts (0-5000mv assuming 5v supply)
        temp1 = temp1 - conversion1;           // convert millivolts tenths of degrees

this works fine, require knowing regulator voltage (regvolt - hardcoded 5000mv)

here's question - how consistent regulator voltage be? how consistent when start changing load (switching on other instruments or leds etc). , how consistent if swap arduinos?

my understand of analogread() returns value proportional both internal voltage , voltage applied pin. if regulator voltage 5v , voltage on analogue pin 2.5 volts return value of 512, if regulator voltage drops 10% value read analogue pin drop 10% if actual voltage applied remains @ 2.5v?

thanks

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