CMOS Oscillator question

The formulas for CMOS oscillators use two constant numbers; 0.405 and 0.693.
Does anyone know where these numbers are derived from?

TIA
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Steve wrote:

http://www.necel.com/en/faq/f_timer.html
-- Sue
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.