# Comparison of NeQuick G and Klobuchar Model Performances at Single-Frequency User Level +
## 3 Results
### SF Position Accuracy  
In Figure 2, SF monthly mean horizontal (HPE 95%) and vertical (VPE 95%) position accuracies are displayed, respectively, for the used stations for the high-/middle north/middle south/low-latitude regions. The position errors are estimated twice, once when the NeQuick G ionospheric model was applied to the positioning solution and another time when the Klobuchar model was applied. The monthly HPE 95% show, in general, smaller magnitudes compared to the monthly VPE 95%, which is mainly the case at high and both middle latitudes, especially for the Klobuchar model. Differences between the GRC, SRC, and NMA/TUW can be seen in the SF position accuracy solutions. This could be explained that each institution uses different kinds of station networks and that different software packages, models, and configurations are applied for the HPE 95% and VPE 95% calculation (see Table 1). At high latitudes (Figure 2) a more-or-less linear trend line of HPE 95% can be noted, which is gradually rising over time and reaching its maximum in April 2022 (beginning of Q2 2022), after which it declines. Before April 2022, the position error is on average 1 m for the NeQuick G model (maximum HPE 95% reached among all the results 2.35 m in 2022 Q2), while for the Klobuchar model values are slightly larger (maximum HPE 95% reached 2.52 m in 2022 Q2). Slightly--but not significantly--larger  
Figure 3: Monthly means of the VTEC error for the NeQuick G and Klobuchar model (NMA/TUW results). The top panel shows results for high latitudes, the middle panel for middle latitudes, and the bottom panel for low latitudes.  
HPE values for the Klobuchar model compared to the NeQuick G model can be observed at mid-latitudes. The low latitudes for both tested models have 2-4 times larger magnitudes compared to the two higher latitude regions. The largest errors are reached in March and April 2022 (end of Q1 2022, beginning of Q2 2022), being \(\approx\)5.5 m for the NeQuick G model and 6.93 m for the Klobuchar model. After those maxima are reached, a rapid decline in monthly HPE 95% at low latitudes can be noticed, approaching the high and middle latitude error values.  
Significantly higher differences in positioning errors between the NeQuick G and the Klobuchar model are reflected in the monthly VPE 95% (Figure 2). Again, a slight linear trend can be recognized at high latitudes for the NeQuick G model (maximum VPE 95% reached 3.5 m in December 2021). On the other hand, the Klobuchar model does not indicate such a trend. The Klobuchar VPEs 95% are throughout the whole period larger compared to the NeQuick G values, with the largest difference being up to 5.36 m in December 2021. The difference between the NeQuick G and the Klobuchar model is also evident at middle latitudes. Moreover, in the case of SRC, for stations located below the 30\({}^{\circ}\) N parallel, in 2021, there is a significant difference between VPE 95% for Klobuchar and NeQuick G, reaching even 4 m in May 2021. There is also a visible difference between the two groups of mid-latitude stations, while the northern ones behave similarly to the high-latitude group, the southern ones have characteristics closer to equatorial stations. The vertical positioning errors from NeQuick G (maximum VPE 95% reached 3.7 m in February 2022) show, as well, for the whole period smaller magnitudes (up to 1 m smaller compared to Klobuchar). The VPE 95% values at low latitudes demonstrate a similar pattern as the horizontal positioning errors for both tested models. In fact, NeQuick G values are on a comparable level (difference 1 HPE 95%-VPE 95% | at low latitudes approximately up to 0.5 m) with the exception in April and May of 2022 (Q2 2022), where the difference between horizontal and vertical errors reached almost 1 m. During the analysed period, Klobuchar VPEs 95% were overall larger compared to the NeQuick G VPE 95% (one exception in March 2022).