It is recommended (Steckl et al., 2004; Abu-Arafeh et al., 2016) to enter a value for the “maximum allowable difference between methods” and choose the option “95% CI of the limits of the agreement”. Bland and Altman indicate that two measurement methods developed to measure the same parameter (or property) should have a good correlation when a group of samples is selected so that the property to be determined varies considerably. Therefore, a high correlation for two methods of measuring the same property could in itself be only a sign that a widely used sample has been chosen. A high correlation does not necessarily mean that there is a good agreement between the two methods. Lin LI, Hedayat AS, Sinha B, et al. Statistical methods for evaluating the agreement: models, problems and instruments. J Am Stat Assoc. 2002;97:257-70. Shieh, G. The adequacy of Bland-Altman`s approximate confidence intervals for The Limits of the Agreement. BMC Med Res Methodol 18, 45 (2018).
doi.org/10.1186/s12874-018-0505-y Carkeet A. Precise Parametric Confidence Intervals for Bland-Altman Compliance Limits. Optom Vis Sci. 2015;92:e71-80. – BAL – p N1.2 – t1 – α/2 (b1.2) and – BAU – z p N1.2 – t1 – α/2 () b1/2. In the particular case of α – 0.05, general expressions are reduced to confidence intervals for the two points of evaluation of the 95% agree limits considered in Bland and Altman : A Bland-Altman diagram (differential diagram) in chemistry or biomedicine is a method of presentation of data used for the analysis of the agreement between two different assays. It is identical to a tube of average difference Tukey, the name under which it is known in other areas, but it was popularized in the medical statistics of J. Martin Bland and Douglas G. Altman.   Choudhary PK, Nagaraja HN.
Measuring compliance in method comparison studies – an audit. In: Balakrishnan N, Kannan N, Nagaraja HN, editor. Investment and selection progress, multiple comparisons and reliability. Boston: Birkhauser; 2004. 215-44. On the other hand, in establishing confidence intervals between the boundaries of agreements or percentiles, Bland and Altman  argued that var[S] ≐ 2/(2) and Var [2) and Var [2) B] ≐ b-2/N, the B-1-for example _p.