Relations become handy when you have to make some sketch in which the dimensions are related to each other with some function even as simple as x=2y. Once relation is created, all dimensions of sketch(s) can be change by changing just one dimension (at least).

The procedure of making relation in sketching is simple.

- First you need to create the required shape.
- Then apply dimension to all the entities upon which you want to apply some relation.
- Then you have to choose the primary dimension from with all other dimensions will be related, remember primary dimension can be more than one.
- Once primary dimension is selected you will have to open relation window so you can specify the relations between dimensions.
- After applying relations only primary dimension(s) will be editable.

### Let’s perform the exercise

Open creo parametric and select the new sketch or part. Then select the front plane and click on sketch icon (if you select the “part” earlier).

Here make a sketch like shown in the following fig. one can see some constraints in the figure. I first make this shape symmetrical using constraint. Then drew an arc.

Due to symmetry and other constraints only 3 dimensions are enough to completely define the sketch.

Now click on “Tools” tab in creo parametric ribbon menu. There find the option named “relation” and click on it.

A new window will open after the click. You will observe that, in sketching window, now the dimensions are labeled with “sd##” for example sd3, sd14 and sd15 in this case.these names may be different in your case. I choose sd15 as my primary dimension and used the following relations.

- “
**Sd14= sd15 / 4″**it mean the small vertical line adjacent to the arc is four time less than the vertical line on right side. - “
**Sd3= sd15 + 150″**it mean horizontal line will be 150 unit greater than the vertical line on right.

Now just change the value of your primary dimension and see the new sketch.it will be updated accordingly.