We buy the computers in year 2019, but it's not fair to say that the € 12.000,- belongs entirely in 2019.
We need to spread the cost over the service life of the computers and that is 3 years.
So not € 12.000,- in 2019 and € 0,- in 2020 and 2021, but
12.000 / 3 = € 4.000,- Depreciation costs in 2019,2020 and 2021