The formula for calculating the effective armor rating in world of tanks is:
Armor tickness/cos(impact angle)
With an Angle of > 70% always leading to a ricochet, this leads to this table:
Impact Angle Effective Armour Thickness
0° 100%
10° 101.54%
20° 106.42%
30° 115.47%
40° 130.54%
50° 155.57%
60° 200%
70° 292.38%
> 70° Ricochet
(source: world of tanks effective armor rating)
Which angle to chose depends a lot on the tank you're driving and how it is armored. But in general, having at least a slight angel towards your opponent is a good idea.
For example, if you're driving a tank with 100mm front armor and 80mm side armor, a 45% angle on both front armor would give you an effective front armor of 141mm and effective side armor of 113mm. In this example having the opponent hit your side at an angle would still give a lower chance of penetration than hitting the front armor at a straight angle.
However if the situation is the same, but the tank you're driving only has 60mm side armor this means the effective rating of the side armor would be 85mm, which means you're giving your opponent an opportunity at an easier penetration, in this case it would be still good to present yourself at an angle, but less than 45%. (a 30% angle in this case would give you 115mm front armor and 120mm side armor)
The "72 xp needed" means that it will take another 72xp to upgrade the skill to the next percentage point. So if your skill was at 11%, then it would take 72xp to get the skill to 12%
Too increase the 1st skill perk to 100% from 0%, you will need a total of total of 210,484 XP.
The World of Tanks wiki describes it in detail:
"It is important to recognize two facts about the amount of XP required to increase Training Level.
First, the total amount of experience required to achieve a 100% Training Level in the 1st Skill or Perk is double that required to increase the Major Qualification to 100%. This doubling occurs each time with each new Skill or Perk. Training the 2nd Skill or Perk to 100% requires double the amount of XP that the 1st Skill or Perk requires, the 3rd requires double the XP of the 2nd and so on. To increase the Training Level of the:"
Major Qualification from 0% to 100% requires a total of 105,242 XP.
1st Skill or Perk from 0% to 100% requires a total of 210,484 XP.
2nd Skill or Perk from 0% to 100% requires a total of 420,128 XP.
3rd Skill or Perk from 0% to 100% requires a total of 840,255 XP.
Best Answer
It happens automatically. If after a battle you have sucessfully fulfilled the requirements and objectives, you will complete the mission. Some missions are limited, others can be completed as much as you like.
The exception to this, are the new personal missions, which behave differently.
You will find these in the upper left corner of your screen, when you are in your garage. You can unlock four new tanks, but in order. In the beginning, only the StuG IV (per time of writing) is available to start unlocking, so when you click on that, you will get a list of missions.
There are fifteen missions for each tank type, and these have to be completed in order. To start a mission, click on it, and there should be a "start mission" button (it will be where the "cancel" button is in the screenshot above). When you have started the mission, it will automatically complete after a battle, so you don't have to worry about it.
When a mission is completed, you have to manually start a new mission as before.