Twister 

By using twister one can mix several qualities and colours. This enables you to compose colours and colour blends to your own taste. Click on "examples"...... 

Shopkeepers using this gadget can twine thin yarns to a thick skein. 

With a minimum amount of stock one can offer a vast assortment.

If you already possess a twister...... Venne-Colcoton Unikat sells some handy aids such as: