Accurate characterization of ionospheric parameters such as total electron content (TEC) and scintillation (signal fluctuation due to ionospheric irregularities) is critical to all users of GPS, whether the ultimate goal is measurement in navigation, geodesy, ionospheric, or atmospheric studies. Improved absolute TEC measurement accuracy is demanded by many global ionospheric characterization schemes, where small errors can be magnified in 3-D tomographic profile reconstructions. We present research showing that there are three errors, or biases that typically result from characterizing TEC with GPS receiver data. These biases are (1) estimation, instead of measurement of receiver differential code bias (DCB); (2) ionospheric divergence of pseudorange-code-derived TEC resulting from code smoothing; and (3) delay of pseudorange TEC as a result of code smoothing. We present results of ionospheric data collected with a receiver that mitigates these biases to demonstrate the utility of improved accuracy, particularly for ingestion into tomographic reconstructions, but also for conversion from slant to vertical TEC.