## 4 Discussion  
We studied the performance of nine ionospheric models in TEC and positioning domains during 2014-2020 (the full data set covered 2000-2020). The main result is that all models perform in a similar way as far as the position domain is concerned (this could be due to noise and other factors (e.g., broadcast ephemeris). The improvement in positioning error against noncorrected solutions was GIM IGSG at 22.0%, BDGIM at 15.3%, NeQuick2 at 13.8%, GEMTEC at 13.3%, NeQuickG and IRI-2016 at 13.3%, Klobuchar at 13.2%, IRI-2012 at 11.6%, IRI-Plas at 8.0%, and GLONASS at 7.3%. While the difference is not high, it is statistically significant. We should also note that instantaneous results should show higher RMS than median ones [(33)]. So, some reasons for the higher RMS in our research is that we used instantaneous coordinates and TEC values. We noticed that the models have a different ranking whether the TEC domain or positioning domain is considered. Yet, the GEMTEC model exhibits the smallest global mean absolute error \(<\!1\,\Delta I\!\,\mathrm{>}\) and the least TEC bias. TEC bias and mean absolute TEC errors are as follows: \(-0.3\) and \(2.4\) TECU for GEMTEC; \(-0.7\) and \(2.9\) TECU for BDGIM; \(-1.2\) and \(3.0\) TECU for NeQuick2; \(-1.5\) and \(3.2\) TECU for IRI-2012; \(-1.5\) and \(3.5\) TECU for NeQuickG; \(-1.8\) and \(3.2\) TECU for IRI-2016; \(1.2\) and \(4.9\) TECU for Klobuchar; \(-1.9\) and \(4.8\) TECU for GLONASS; \(3.1\) and \(4.2\) TECU for IRI-Plas. Different scientists used the positioning domain along with the TEC domain to assess the model performance [28; 34]. [PERSON] et al. [34] clearly formulated the advantage of such an approach. Using data for the year 2014 and 34 permanent stations, they calculated both residual dual-frequency slant TEC (that is carrier-to-phase leveled) vs. GIM TEC and positioning error in PPP single-frequency solution involving GIM IGSG and GIM UQRG. The measurement noise, pseudo-range multipath, evaluation metric, and outliers are the main problems in the models' evaluation, and if one takes them into account, then positioning and TEC domain are close [34; 35]. The technique allowed the authors to reveal that GIM UQRG is better than GIM IGSG both in TEC and positioning domains. We did not perform carrier-to-phase leveling and used a standard non-smoothed coordinate solution with a broadcast ephemeris because this reveals the real problems in standard positioning that appear for most users. We compensated for this decrease in sensitivity with a huge data amount (6 years to compare all the models together and 20 years for older models). Usually, the models were tested for a rather limited time period and region covering. [PERSON] et al. [28] used only the 22 nd day of each month from 2001 to 2011 to test the Klobuchar and GEMTEC models and found that they eliminate about 57 and 85% of the absolute error. Tables 2 and 3 also demonstrate that the GEMTEC model performs better than the Klobuchar model. We should note that in the TEC domain, GEMTEC is one of the best models. [PERSON] et al. [36] showed that GEMTEC overperformed the Klobuchar model for 2003-2012 (at the Asian mid-latitudes). Because GEMTEC is a GIM-based model involving data up to 2012, we could expect a reduction in its precision after that period. [PERSON] et al. [37] showed that GEMTEC overperformed NeQuick2 and especially Klobuchar models for 2017. Current results show that GEMTEC keep good quality after 2012 and overperformed IRI and NeQuick sets after 2012 until 2020 at almost the same level as before. Several studies found that the IRI-Plas model overestimates TEC [38]. [PERSON] et al. [39] comprehensively studied the NeQuick2 and IRI-Plas over the whole solar cycle (2006-2017) based on 36 globally distributed stations (we used three of those stations in our set). The NeQuick2 overperformed IRI-Plas in the TEC domain except for several locations (three stations in the African-Asian sector).