Lithium abundance according to the effective temperature for Montréal/Montpellier models (model set 1, left panel) and CESTAM models (model set 2, right panel) at 12.5 Gyr, taking into account different T₀ values for the parameterized turbulent diffusion coefficient. The corresponding Δ values are shown on the right y-axis. The gray symbols are observed lithium abundances from Sbordone et al. (2010) (circles), Bonifacio & Molaro (1997) (triangles), and the SAGA database (http://sagadatabase.jp/, Suda et al. 2008, 2011; Yamada et al. 2013; Suda et al. 2017) (squares). The black square with error bars represents the standard value for the lithium plateau (Sbordone et al. 2010). The green area represents the range of Δ values found in Sect. 3.