An instant thermometer is not only more accurate but also makes a thinner hole in the meat. Fewer of the meat's internal juices, therefore, can exit through that aperture. Although it is true that you make many holes when using an instant thermometer
, as opposed to only one with the larger instrument, these holes are so small that they quickly seal themselves.
Because you leave the larger type of thermometer in the meat as it roasts, heat is quickly conducted to the flesh surrounding the metal spike. This rapid heat transfer cooks the meat surrounding the spike faster than it should, and, consequently, uneven roasting occurs. A small instant thermometer does not pose this problem because it is not left in the roasting meat. (If it were, the mechanism will be ruined).
A frequently overlooked advantage of a small instant thermometer is that it allows you to test-probe the meat in more than one place.
** Types of Thermometers