how to caluculate ccpu_exp value for 1 second time value?

[nagesh]

How to find the ccpu_exp value for 1 second? @ kern_synch.c

Decay 95% of proc:_pctcpu in 60 seconds, ccpu = exp(-1/20) */
const fixpt_t ccpu = 0.95122942450071400909 * FSCALE;

0.60653065971263342360 * FSCALE, /* exp(-1/2) : decay 95% in 5s */
0.95122942450071400909 * FSCALE, /* exp(-1/20) : decay 95% in 60s */
0.98347145382161748947 * FSCALE /* exp(-1/60) : decay 95% in 5m */

What will the value for 1 second, Is there any formula to calculate the value.