Most of publications before the catastrophe were easy to be identified. The printing skills of people before the catastrophe could not be surpassed by people of today at all. Many books in that age contained delicate images or photos, at the sight of which, people would know which age those particular books belonged to. What concerned that roughly printed book "Mental Arithmetic by Abacus" that Zhang Tie had bought from a roadside booth in the railway station which only had a few pages with no pictures except for an abacus on its cover, Zhang Tie was definitely very lucky to own it.