millis or micros has a time delay phenomenon?

There is nothing in the loop except only time function.
At first, it can be seen to work constantly on time.
But, it gets more and more time to work.
Why is this happening?

You can refer to the pictures I attached.
(figure 1. code, figure 2. The excel picture shows how long the interval has occurred.)

What do you expect? You are outputting 960 characters per second. If you output two characters before the decimal point, the decimal point, two characters after the decimal point, the carriage return and the line feed then you are outputting 7 characters per line. This takes over 7 milliseconds once the internal buffer is filled.

Why are you measuring in microseconds when your program is taking nearly 10 milliseconds?

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You are stuffing characters into the serial buffer faster than they can be sent. Once the buffer is full, each character being put into the buffer will have to wait for a character to be sent.

It takes about a millisecond to send one character at 9600 baud (10 bits: 1 start, 8 data, 1 stop). When you are sending about six characters per line the delay is 6.24 milliseconds. When you are sending about seven characters each time through loop() it makes sense that your timer will have intervals of 7.28 milliseconds. It looks like it takes 1.04 milliseconds per character.

Adding to the helpful comments above- careful use of micros() should be studied; see Nick's reply.

I have no intention of trying to read code that is posted as a picture. Post your .ino file.

…R

I save a variable to an array and when the array is full, stop the test and print the results.
reset and repeat.

unsigned long loopTime [50];  // An Array To hold the loop test times
byte loopNum;  // Index for the Array
unsigned long oldLoopTime; 
int delayTime = 5;

void setup() {
  Serial.begin (9600);
}

void loop()
{
  loopTime [loopNum] = micros();  // Record the time
  loopNum++;  // Increment the Index
  if (loopNum >= 49)  // when the array is full
  {
    loopNum = 0;  // reset the Index
    testResults();  // call a function to print the results
  }
  delay (delayTime);  // slow things down a little. We will subract this from the result
}

void testResults()  // do the math and print the results
{
  for (byte i = 0; i <= 49; i++)
  {
    unsigned long result = (loopTime[i]- oldLoopTime)-(delayTime*1000);
    Serial.println(result);
    oldLoopTime = loopTime [i];
  }
}

Also, 9600 baud is kind of slow. You might want to try changing your program (and setting your Serial monitor) to use a higher baud rate.