Measuring Gas Pressure
Key Questions

Gas Pressure is measured in a variety of units.
Standard Temperature and pressure call for one atmosphere (1 atm) at
#0^oC# which is 273 K.According to the wok of Evangelista Torrcelli, at sea level, 1 atm of air pressure will sustain a column of mercury at 760 mm meaning
1 atm = 760 mmHg or 1 atm = 760 torr (torrcellis)
In physics, the measure is completed in units called Pascals where 1 atm of gas is equivalent to 101,325 Pa or 101.3 kPa (kiloPascals).
In the United States where the System International (SI) is still just a fad, we can still find pressure in pounds per square inch or psi.
I hope this was helpful.
SMARTERTEACHER 
Boyle's Law is a relationship between pressure and volume at a constant temperature.
#P_1V_1 = P_2V_2# In this relationship, pressure and volume have an inverse relationship when temperature is held constant.
If there is a decrease in the volume there is less space for molecules to move and therefore they collide more often, increasing the pressure. If there is an increase in the volume the molecules have more space to move, collisions happen less often and the pressure is decreased.
vV ^P ^V vP the relationship is inverse.
If temperature is changes then the gas law involved would be the combined gas law which incorporates all three values and the temperature and volume would both have an effect on the pressure.
#(P_1V_1)/T_1 = (P_2V_2)/T_2# I hope this was helpful.
SMARTERTEACHER 
Boyle's law studies the relationship between pressure and volume. It's an inverse relationship as it is indicated that when pressure increases, volume decreases and viceversa.
It can be summarized as...
#P_1V_1 = P_2V_2# Here is a video which shows an example of how you can solve a gas problem using Boyle's law.
video from: Noel Pauller