I went to DIY Supermarket the other day to look for a new pillow, the neck pillow to be exact. There was a pillow that took my attention away from the others, a white pillow with a few stripes of blue sky colour. I could not find any price tag on the display rack nor the pillow itself but luckily there is the barcode tag attached on the pillow. As far as I know, when there is only barcode tag attached on an item, I can check the price at the counter or use any price checker available around the supermarket. Maybe it was my lucky day because the price checker was just beside the rack. So, I took the pillow with me and placed the barcode tag correctly, just below the price checker where a red laser is being emitted. It takes me a few seconds to scan the barcode since the laser is very limited to a specific size and distance to detect the barcode. There was a beep sound, notifying that the barcode has been scanned and the interface displayed the name, ID and the price of the pillow. This case study can be related to one of the fundamental design principles which are Constraints.