Verilog time format

timeformat.v

//To change the way (below) is displayed
$display("%t", $realtime);

//$timeformat(unit#, prec#, "unit", minwidth);
$timeformat(-3, 2, " ms", 10);    // -3 and " ms" give useful display msg

unit      is the base that time is to be displayed in, from 0 to -15
precision is the number of decimal points to display.
"unit"    is a string appended to the time, such as " ns".
minwidth  is the minimum number of characters that will be displayed.

  0 =   1 sec
 -1 = 100 ms
 -2 =  10 ms
 -3 =   1 ms 
 -4 = 100 us
 -5 =  10 us
 -6 =   1 us 
 -7 = 100 ns
 -8 =  10 ns
 -9 =   1 ns 
-10 = 100 ps
-11 =  10 ps
-12 =   1 ps 
-13 = 100 fs
-14 =  10 fs
-15 =   1 fs 

//Source
//http://www.sutherland-hdl.com/online_verilog_ref_guide/vlog_ref_top.html