What should the frequency reading of the SPI clock be with this code?

My Extech EX330 multimeter is reading 3.439Mhz on the pin 13 on my Arduino Uno running the following code. Is the reading correct? If the divider is 2, shouldn’t I get 8 Mhz (16Mhz / 2)?

#include <SPI.h> 
void setup()
  pinMode(13, OUTPUT);

  digitalWrite(13, HIGH);
void loop()

  byte pot = B0;                
  SPI.transfer(pot);                        //  Do SPI transfer of variable pot