Thanks Byyp for your explanation ...

But I have a blog having 400 impressions per day ..

Sometimes I get 10 clicks per day but I only manage to earn a total of 10-30 cents day for the total clicks. Today I got 3 clicks Page CTR = 1.35% & Page eCPM $1.05 which brings my earning to 23 cents for 3 clicks Why this variations ???