var pmt_mx=16;
var pmt_old=0;
var pmt_akt=1;
function pbx(n){
  pmt_old=pmt_akt;
  pmt_akt=pmt_akt+n;
  if(pmt_akt<1) pmt_akt=pmt_mx;
  if(pmt_akt>pmt_mx) pmt_akt=1;
  pmts();
}
function pmts(){
  if(pmt_old!=0) document.getElementById('PMIT'+String(pmt_old)).style.visibility="hidden";
  document.getElementById('PMIT'+String(pmt_akt)).style.visibility="visible";

}