Inconsistent pricing

I find it difficult to understand why the quarterly subscription results in a unit price of 3.07€ when the yearly subscription results in a unit of 3.52€.
Also the unit price of single units (7.99€) is a bit too expensive in my opinion and regularly discourages me to purchase a unit that I would find of interest

TibDubai about The Economist weekly EU iPad, v3.1.7