I've been reading different articles about oscillators, or more specifically, multivibrators. To find the frequency, you divide 1 by the time constant of RC. I thought the formula for the time constant was simply R x C. But some articles said it was 2.2 x R x C or 2.3 x R x C or .693 x R x C or even 2 x pi x R x C. There might be others I haven't come across yet. Can someone explain this to me please? Thanks in advance