Significant difference between millis() and micros()

when run code below , change between millis() , micros() there quite variance
with millis() time shown varies between 2 , 3 milliseconds.

however if change micros(), time shown 8700 micro seconds or 8.7 milli seconds.

can explain why big difference ?

code: [select]

void loop()
{
//start timer
gettime_millis = millis();    //micros();

drawscreen1();     //draw on tft screen

//calculate time taken loop
newtimemillis = millis();    //micros();
timelapsemillis = newtimemillis-gettime_millis;

//need bit of time see result
delay(1000);

} 

with such short times, can imagine happen.
the millis() not accurate few milliseconds (read: inaccurate). updated in interrupt.
we don't have whole sketch, don't know if did use right variable types.

perhaps can try drawscreen1() in loop , 20 or 100 times. millis() , micros() should measure same delay.

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