Exercise One.
Take a simple thought for example health, think of yourself in full health, think of that warm glow, the relaxed feeling you have when you're feeling healthy. Try to maintain this thought for as long as possible, don't let other thoughts intrude, concentrate completely upon yourself. This is a good exercise to start with as it is not too specific, it will allow only thoughts and images about yourself to intrude upon your mental process.

Exercise Two.
Hold your arm out in front of you at shoulder height. Raise your hand slightly so you can see your fingernails, concentrate upon your fingernails trying to keep your arms steady for at least one minute. Each time you perform this exercise try to extend the concentration time a little longer until performing the exercise for up to five minutes. Do this exercise with both arms.

Exercise Three.
Take a glass of water and hold it in front of you, fix your attention upon the top of the glass. Try to keep your arm as steady as possible, concentrate upon the ripples: your aim is to see no ripples, no movement within the water at all.

Exercise Four.
This exercise can be performed by either standing or sitting. Take a piece of plain paper and draw a visible dot in the center, place the paper on the wall in front of you and concentrate upon the dot. When you are relaxed, imagine the air that you are breathing in is coming from the dot and the air you are exhaling is going into the dot. Start performing this exercise for at least five minutes and increase up to at least 20 minutes.

Exercise Five.
There is no time limit set upon this particular exercise, but if practiced on a regular basis can open your mind to its inner potential. Take a clock, one you can hear the ticking, your aim is not to concentrate upon the ticks, but upon the spaces between the ticks. As you gain experience with this exercise you may well notice that the ticks begin to dissolve in your mind and the time between the ticks becomes extended. But the longer you can perform this exercise and the deeper you can concentrate while doing it, your perception of time begins to disappear, the exercise is completed in no time at all.

It is only after an extensive use of these exercises that we begin to appreciate the benefits of concentration, like learning to ride a bike once we have mastered the Art it is something that never leaves us

http://www.trans4mind.com/counterpoint/bulger.shtml

Use this formula: D= (Pd/Rd*T) + (Pv/Rv*T)

where: D = density, kg/m3
Pd = pressure of dry air, Pascals
Pv= pressure of vapor, Pascals
Rd = gas constant for dry air, J/(kg*degK) = 287.05
Rv = gas constant for vapor, J/(kg*degK) = 461.495
T = temperature, degK = deg C + 273.15

Use the formula and calculate yourself.