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.
Many tank destroyers, and particularly the Stug III have a great camo rating, which means that if you play carefully the enemy team will have great difficulty spotting you.
While playing this particular tank, and other TDs like it, try to stay behind the rest of your team and lay down supporting fire form a sniping position.
If you're not familiar with how camo and spotting works, I recommend this camouflage tutorial.
Some general tips:
- Stay behind a bush, but remember that firing your gun will temporarily remove the additional camo value of the bush
- Equipping your TD with a camo net, and training the crew in camouflage will greatly increase your overall camo rating.
- Remember that moving your tank, even by slightly turning it lowers your camo value. With TDs and SPGs you can prevent accidentally turning your tank by locking it in place by using the (default) X key.
- The commander's sixth sense skill is great on TDs as it will help you know when you're spotted.
- The Stug III is responsible fast and mobile, if you are spotted or think you might be soon, relocate to a new position from which you can safely snipe.
Best Answer
While I'm not a huge fan of playing arty, I've done a bit of counter battery fire in patch 9.12 and 9.13. While there still are arty tracers (just like there are shell tracers for all tanks) arty tracers are nowhere near as obvious as they used to be. In recent patches, a tracer will be seen as a tiny white steak departing the arty's location very quickly. Tracers are quite hard to spot, and even harder to find the exact point of origin of. So while counter battery fire is still a viable strategy, I wouldn't recommend it unless you are already experienced, especially since long range accuracy is so rng dependent. However, if you really have your heart set on cb fire, listen closely to the sounds- there will be a telltale "whiff" sound when arty fires in the region you're looking at.