( Test routine for Parallax PING UltraSonic sensor model 28015 ) 
: PING 
    TC0 OFF TC0 ON TC0 OFF ( output a single pulse, low-->high-->low from TC0  
    TC0 SET-PWM-IN         ( set up TC0 as input to measure the pulse 
    BEGIN 
     CHK-PWM-IN ?DUP UNTIL 
     444 / . ." in "       ( take the raw number divide by 444  
;                          ( to get the unit in inches