# In Geometry nodes, why do I need to define the scale attribute before it can be used?

Using the scale attribute in the Attribute Vector Math node causes the error "No attribute with the name scale". However, if I add a Point Scale node, it works.

On the other hand, if I were to just use the Attribute Mix node or an Attribute Math node, I do not need to use a Point Scale to achieve the same results.

Why is the Attribute Vector Math behaving this way? Image 1 : Attribute Mix

Image 2 : Point Scale and Attribute Vector Math

Well, you need to define it because… It does not exist.

This is defined in documentation:

If the attributes don’t exist yet, a default value is used, which can depend on the situation. For example, in the Point Instance Node, the default value for scale is a unit scale of (1, 1, 1)

https://docs.blender.org/manual/en/latest/modeling/geometry_nodes/attributes_reference.html#naming-conventions

So the Scale attribute doesn't exist, and the default value is used. In your case, you can do several things:

1. Put Scale as a result of math operation. B value should be a static vector. This will create attribute Scale

2. Don't use dist at all, use Scale from the beginning and manipulate with it.

• IMO, this is very counter-intuitive. Yukky. BTW, should we be careful to call it scale? It's Scale in the spreadsheet, but scale if you type it in. Another gotcha. Aug 31 '21 at 11:05
• Thank you for the reply but I still do not understand. Why does Attribute Math / Attribute Mix work but not Attribute Vector Math? If "scale" doesn't exist yet, then shouldn't Attribute Math and Attribute Mix give the same error? sorry, its still not clicking for me. Aug 31 '21 at 11:09
• It's looks like Attribute Vector Math doesn't know about default value, maybe. So it's looks like a small design fault in GN development (Anyway it should be redesigned in 3.0). I believe you should create this attribute properly to make sure that it is exists, and every node will behave in the same way. Aug 31 '21 at 11:14
• @RobinBetts I have seen a plan to redesign this in 3.0 with scale input socket, so it should be more intuitive. Aug 31 '21 at 11:17