ADC sampling rate doesn't tally with sampling rate calculated from plot

Using Arduino Sensors
3

here is the source code for the Serial object:
./hardware/arduino/cores/arduino/HardwareSerial.h
./hardware/arduino/cores/arduino/HardwareSerial.cpp

u could try to use time slots by using micros() like this:

uint32_t last = 0;
void loop() {
  for (;;) {
    const uint32_t now = micros();
    if (now-last >= 1000) {
      last = now;
      break;
    }
  }
  analogRead...
  Serial.write...
}

1kSps (10bits payload + 5bit error detection + 1bit high/low byte = 2B/sample = 16kbit/sec) should be ok on a 115200kbit/sec link...