To calculate the perimeter of the given shape, we'll add up the lengths of all its sides.

From the image:

• The top three horizontal segments measure 18 mm, 8 mm, and 20 mm.
• The two vertical segments on the right are 23 mm each.
• The three vertical segments on the left are 45 mm, 23 mm, and 45 mm.
• The bottom three horizontal segments are 10 mm each.

Now, let's add these up:

1. Top horizontal sides:

   • $18 \text{ mm} + 8 \text{ mm} + 20 \text{ mm} = 46 \text{ mm}$

2. Right vertical sides:

   • $23 \text{ mm} + 23 \text{ mm} = 46 \text{ mm}$

3. Left vertical sides:

   • $45 \text{ mm} + 23 \text{ mm} + 45 \text{ mm} = 113 \text{ mm}$

4. Bottom horizontal sides:

   • $10 \text{ mm} + 10 \text{ mm} + 10 \text{ mm} = 30 \text{ mm}$

Finally, sum up all the sides to find the perimeter:

$P = 46 \text{ mm} + 46 \text{ mm} + 113 \text{ mm} + 30 \text{ mm} = 235 \text{ mm}$

So, the perimeter of the shape is 235 mm.

Would you like any further details or explanations?

Here are some related questions:

1. How would you calculate the perimeter if the shape had more indentations?
2. What is the perimeter of a shape with similar dimensions but without indentations?
3. How does the unit of measurement affect the calculation of the perimeter?
4. What is the difference between finding the perimeter of a 2D shape versus the surface area of a 3D shape?
5. How would you find the perimeter of a complex polygon with more sides?

Tip: When dealing with complex shapes, break the shape into simpler parts to make calculating the perimeter easier.