by thenewage
How deep is 3 bars and could you use a watch that is limited to 3 bars for any serious diving?
ScubaDivingFanClub Answer:
The answer to your question is: 3bars = 20 meters or 66 feet. Now we will explain how we came up to this response.
A French philosopher and scientist named Blaise Pascal demonstrated that the pressure applied by the atmosphere at sea level is equal to the pressure applied by approximately 10 meters / 33 feet. It means that for each 10 meters / 33 feet of sea water, we will have to add 1 atmosphere.
When doing calculation on depth and the pressure we have to take into account that at the surface there is already one atmosphere. And also to get to the measuring system you feel comfortable with you have to know that 1 ATM=1.01 BAR and to make it more simple 1ATM=1BAR.
Depth 
Pressure 
0  1 ATM/BAR 
10M/33F  2 ATM/BAR 
20M/66F  3 ATM/BAR 
30M/99F  4 ATM/BAR 
40M/131F  5 ATM/BAR 
50M/164F  6 ATM/BAR 
60M/197F  7 ATM/BAR 
70M/231F  8 ATM/BAR 
80M/264F  9 ATM/BAR 
90M/297F  10 ATM/BAR 
100M/330F  11 ATM/BAR 
150M/495F  16 ATM/BAR 
200M/660F  21 ATM/BAR 
Continuing with an answer to your question  to take a watch for recreational diving, these watches must be at least minimum 50M/164F or 6 ATM/BAR water resistant.
But I have a little story for you: I was doing a deep dive (30M/100F) with students doing PADI Advanced Open Water, and my diving watch had no battery. I needed a watch just to take the time of the dive and for the mandatory 3 minutes safety stop.
Going to work that day I decided to buy a cheap 100 meters digital watch just until I replace a battery in my diving watch.
Everything went well on the deep dive until we started the safety stop, I looked at that cheap peace of …100M watch and the crystal was gone, the watch filled up with water and I had to rely on one of my student’s watch for the safety stop and dive time.
Most watches have a 200 meters water resistance. I guess the following proverb applied to my purchase: "you get what you pay for".
Thank you for visiting our web site. We hope this answers your question and feel free to send any additional questions or concerns.
Have fun diving, Sincerely:
ScubaDivingFanClub
Where Scuba Divers share their passion.
Some corrections have being made
We would like to thank our "Anonymous” visitor for his/her comment (see comment below). Yes there is some misunderstanding when we were trying to explain Blaise Pascal demonstration of pressure applied by the atmosphere. We will try to clarify and make it easier for our visitors to understand.
A French philosopher and scientist named Blaise Pascal demonstrated that the pressure applied by the atmosphere at sea level is equal to the pressure applied by approximately 10 meters / 33 feet. It means that 10 meters / 33 feet will be equal to 1 atmosphere.
Statement:
It means that 10 meters / 33 feet will be equal to 1 atmosphere.
Clarification:
It means that for every additional 10 meters / 33 feet of sea water, we will have to add 1 atmosphere.
Since at sea level, 0 meter / 0 feet = 1 ATM/BAR.
At 10 meters / 33 feet = 2 ATM/BAR
Hence, at 20 meters / 66 feet = 3 ATM/BAR
Hope this helps.
ScubaDivingFanClub
Where Scuba Divers share their passion.
Jun 02, 2010 
Clarification:
Clarification: 
May 07, 2010 
Your math sucks! 3x33 does not = 66. haha by: Anonymous Your answer to his question that 3 bars= 66 feet is wrong when you state in " How you got this" it shows 1 bar / ATM (atmosphere) equals 33 ft. Well 3 ATM multiplied by 33 ft as shown in your shart below equals 99ft., not 66ft. 

To the guys who didn't get it. (who said your math sucks)
by: Anonymous
Actually he has it right. At Zero(0) depth as in when your head is above the water you are at one(1) Atmosphere. Once you go down 10 meters/33 feet that is equivalent to having another atmosphere above you, adding up to a total of two(2) atmosphere. When you see the chart (See Below) maybe it'll help me explain better.
So 3 Bars = 20m/66F = 3 ATM/BAR
Bar Depth Pressure
1 0 1 ATM/BAR
2 10M/33F 2 ATM/BAR
3 20M/66F 3 ATM/BAR
4 30M/99F 4 ATM/BAR
5 40M/131F 5 ATM/BAR
6 50M/164F 6 ATM/BAR
7 60M/197F 7 ATM/BAR
8 70M/231F 8 ATM/BAR
9 80M/264F 9 ATM/BAR
10 90M/297F 10 ATM/BAR
11 100M/330F 11 ATM/BAR
12 150M/495F 16 ATM/BAR
13 200M/660F 21 ATM/BAR