if a==1
  set(he2,'Enable','on');
  set(tx5,'Visible','on');
  set(he1,'Enable','off');
  a=a+1;
elseif a==2
  set(he3,'Enable','on');
  set(tx6,'Visible','on');
  set(he2,'Enable','off');
  a=a+1;
elseif a==3
  set(he4,'Enable','on');
  set(tx7,'Visible','on');
  set(he3,'Enable','off');
  a=a+1;
else
  set(pu1,'Enable','on');
  set(tx8,'Visible','on');
  set(he4,'Enable','off');
  a=1;
end