Percent difference (DIFF%) $$DIFF\% = \left[ {\left( {\frac{{BHT_{CALC\left( i \right)} - BHT_{m\left( i \right)} }}{{BHT_{m\left( i \right)} }}} \right) \times 100} \right]$$ (6) García-López et al. (2014)
Root mean square error (RMSE) $$RMSE = \sqrt{{\frac{1}{n}\mathop \sum \limits_{i = 1}^{n} \left( {BHT_{m\left( i \right)} - BHT_{CALC\left( i \right)} } \right)^{2} }}$$ (7) Willmott et al. (2009)
Mean absolute error (MAE) $$MAE = \frac{1}{n}\mathop \sum \limits_{i = 1}^{n} \left| {BHT_{m\left( i \right)} - BHT_{CALC\left( i \right)} } \right|$$ (8) Wang and Lu (2018)
Mean absolute percentage error (MAPE) $$MAPE = \left( {\frac{1}{n}\mathop \sum \limits_{i = 1}^{n} \left| {\frac{{BHT_{m\left( i \right)} - BHT_{CALC\left( i \right)} }}{{BHT_{m\left( i \right)} }}} \right|} \right) \times 100$$ (9) Li and Shi (2010)
Difference coefficient (Theil's U) $$Theil^{\prime}s U = \frac{{\sqrt{{\mathop \sum \nolimits_{i = 1}^{n} \left( {BHT_{m\left( i \right) - } BHT_{GaS\_GeoT\left( i \right) } } \right)^{2} }}}}{{\sqrt{{\mathop \sum \nolimits_{i = 1}^{n} \left( {BHT_{m\left( i \right) - } BHT_{GasGeo\_Lit\left( i \right) } } \right)^{2} }}}}$$ (10) Álvarez del Castillo et al. (2012)