Step 1 :
Divide $ 213 $ by $ 79 $ and get the remainder

$$ 213 : 79 = 2 \text{ ( remainder is } \color{blue}{ 55 } \text{ ) } $$

The remainder is positive ($ 55 > 0 $), so we will continue with division.

Step 2 :
Divide $ 79 $ by $ \color{blue}{ 55 } $ and get the remainder

$$ 79 : 55 = 1 \text{ ( remainder is } \color{blue}{ 24 } \text{ ) } $$

The remainder is still positive ($ 24 > 0 $), so we will continue with division.

Step 3 :
Divide $ 55 $ by $ \color{blue}{ 24 } $ and get the remainder

$$ 55 : 24 = 2 \text{ ( remainder is } \color{blue}{ 7 } \text{ ) } $$

The remainder is still positive ($ 7 > 0 $), so we will continue with division.

Step 4 :
Divide $ 24 $ by $ \color{blue}{ 7 } $ and get the remainder

$$ 24 : 7 = 3 \text{ ( remainder is } \color{blue}{ 3 } \text{ ) } $$

The remainder is still positive ($ 3 > 0 $), so we will continue with division.

Step 5 :
Divide $ 7 $ by $ \color{blue}{ 3 } $ and get the remainder

$$ 7 : 3 = 2 \text{ ( remainder is } \color{blue}{ 1 } \text{ ) } $$

The remainder is still positive ($ 1 > 0 $), so we will continue with division.

Step 6 :
Divide $ 3 $ by $ \color{blue}{ 1 } $ and get the remainder

$$ 3 : \color{blue}{ \boxed { 1 }} = 3 \text{ ( remainder is } \color{blue}{ 0 } \text{ ) } $$

The remainder is zero => GCD is the last divisor $ \color{blue}{ \boxed { 1 }} $.

This solution can be visualized using a Venn diagram.

The GCD equals the product of the numbers at the intersection.

GCD Calculator