The GLBVBD tolerance sets the default variable bounds while the global solver is running.  If this parameter is set to d, then variables will not be permitted to assume values outside the range of  [-d, d].  Setting this parameter as tightly as possible in the Value Field restricts the global solver from straying into uninteresting regions and will reduce run times.  You may also need to set the GLBUBD tolerance to control how the global solver uses the bound.  The default value for GLBVBD is 1.e10.