Kelvin probe force microscopy (KPFM, also known as surface potential microscopy) measures the work function, or electric potential, of materials or charges on the nanometer length scale. Despite much effort, KPFM has suffered from its inability to obtain consistent measurements of absolute work-functions in ambient conditions. Contamination, oxidation, and tip-induced electrochemical reactions are all at play and make repeatable quantitative measurements a daunting challenge. Even under ultra-high vacuum, tip-wear can lead to large measurement uncertainty both over time and from probe to probe. In our new probe and instrument designs, we have found ways to reduce probe to probe measurement scatter to below a standard deviation of 50 mV. This represents a major advance towards quantitative work function measurement, which in turn expands KPFMs utility in ever demanding applications.