I know 1RC is when the voltage across the capacitor has reached approx. 63% of Vs. In multivibrator transistor circuits I see the time constant multiplied by 0.7. I know 0.7V is the switching on voltage for a BJT. Is this why 0.7 is used? But Ive seen CMOS ics circuits use 0.7 in multivibrator/timing circuits CMOS use FETS not BJT.