The TWL predicts the maximum level of work that can be carried out in a given environment, without workers exceeding a safe core body temperature 38.2 °C (100.8 °F) and sweat rate (< 1.2 kg or 2.6 lb per hour). WBGT does not incorporate a direct measure of wind speed and requires estimation of metabolic rates, which can have a margin of error up to 50%. Heat stress indexes such as WBGT and ISO 7933 do not take into account the effects of long hours of hard work, dehydration, or the impact of personal protective clothing and equipment. WBGT and heat index are too conservative and inappropriate for practical in the extreme working environments such as Middle East countries or high-temperature process industry or mines. Scarlet TWL-1S incorporated both WBGT and TWL index features. You can simply switch heat indices for your need.