Unless someone printed this weekly tip out for you, you are using a computer right now.
How are you sitting?
Are you comfortable?
What is the angle of your neck?
How is your back aligned?
If you keep sitting this way for another 30 minutes, will you still be comfortable?
Did you change your posture as you read those questions?
What posture feels better for you?
The link shows you a diagram with the key points about how to sit when using a computer so that you avoid the postural conditions that so many computer users develop.
Compare how you are sitting right now with the diagram.
My best wishes, Paul