We already wrote about how the skill system will be realized. It is necessary to clarify how they will increase skills levels and that will affect.
Skills, as well as the objects to which they apply - will have a levels. Colour will tell the success rate.

Red. The difference between the skill level and the subject is more than 5. Chance of successful use - 0%.

Orange. Skill Level 5 (or lower) below the level of the object. There is a chance of successful use, and with an increased bonus experience. In this case, almost twice increased stamina consumption and damage to the instrument (for failing to use). The smaller the difference in the level - the higher the success rate, lower fuel consumption, damage the instrument and the resulting experience.

Yellow. There is no difference in level or skill level of the object is slightly higher than the level of the object (1-4). Ability is always applied, but without the additional experience. With a big difference - experience lower, but increases the speed and number of resources. Reduced consumption, damage the instrument and the resulting experience.

Green. Skill Level 5 above object level. Ability is also applied always, but the resulting experience is even lower. All other bonuses are increased to the maximum. The costs are minimal.

Gray. Skill Level 6 (or more) above the level of the object. Experience is not given, all the rest is similar to the previous one.

Also, there will be a quality system for the equipment. If the object is below 100% quality, the basic values are worse, if the above - increased. The minimum quality value of 50% and maximum 150%.
The quality is also dependent on the difference in the levels of skills and the object.
Red - 0%
Orange - from 50% to 112%
Yellow - from 80% to 144%
Green - from 90 to 150%
Gray - from 90 to 150%