I hate lugging around the car seat when I have an infant. That is why it is called a car seat.... I only want to use it in the car. So when I want to go grocery shopping this, the Baby Shopper, allows me to put my little one in the shopping cart seat when they are still wobbly.
The pattern has printable pattern pieces, detailed instructions, and photos of most of the steps.
Some people have used this for a portable highchair. I have also added ties to it so people can use it in their vintage style wooden highchairs, so that there is a cushion and restraint.
It is not in metric, but there are few measurements needed. It is a very forgiving pattern, meaning it doesn't have to be made exact to function.