As altitude increases, the available amount of oxygen to sustain mental and physical alertness decreases with the overall air pressure, though the relative percentage of oxygen in air, at about 21%, remains practically unchanged up to 21,000 metres (70,000 ft).
  State legislators in Texas (both representatives and senators) make a salary of $7,200 per year.
The 535 members of the current Congress earn a sizable salary, although a few other federal officials are paid more. Certain senators and representatives are quite wealthy. In 2011, a United States senator earned $174,000 per year. This rate was established in 2009 and was an increase from the prior salary of $169,300. In 2000, senators earned $141,300 per year. In 2011, members of the House of Representatives earned $174,000 per year, an amount identical to the salaries of the senators.