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tokens: 1 ). We extracted photometry for point sources in each individual image to construct light curves of Sgr A* and calibration stars. The brightness and position of all sources were measured using the point spread function (PSF)-fitting software StarFinder (Diolaiti et al. 2000 ). Details on running StarFinder on individual frames for Galactic center observations can be found in Do et al. ( 2009 ). Sgr A* is detected in almost every frame of observations on three nights. There are fewer detections of Sgr A* on 2019 May 19 due to lower-quality AO correction and faint flux levels for Sgr A*. We calibrate the point source photometry using reference stars defined by Gautam et al. ( 2019 ). We convert between K ′ magnitudes to absolute fluxes F , using the relationship mJy (Tokunaga Vacca 2005 ). To convert from K ′ fluxes to K s fluxes, we use the filter transformation computed for the color of Sgr A* (Chen et al. 2019 ). We will mainly use observed fluxes in this work to avoid confusion with the value of extinction to apply. To de-redden the flux measurements, one can use the relationship . To compare to fluxes from (Witzel et al. 2012 ), use (Schödel et al. 2010 ). We estimate the Sgr A* relative photometric uncertainties by using the relationship between flux level and flux uncertainty of nearby stars. The photometric uncertainties for stars on each night were determined by using the standard deviation of their individual flux measurements. We find that the reference stars are stable during the nights with 3% photometric errors. Following Do et al. ( 2009 ), we fit a power-law to the relationship between flux level and flux uncertainty for stars within 1′′ of Sgr A*. We then use this relationship to infer the flux uncertainty for the all flux measurements of Sgr A*. The Sgr A* relative photometric uncertainties are typically less than 5% at high flux levels and about 15% for faint flux values. 3. Results Our observations show Sgr A* to be highly variable in 2019. On 2019 May 13, Sgr A*'s flux level changed by a factor of 75 within 2 hr (from 6.19 ± 0.08 mJy to 0.08 ± 0.01 mJy). The maximum observed fluxes occurred during the beginning of the observations, suggesting that Sgr A* was likely even brighter earlier in the night. On the night of 2019 April 20, Sgr A* flux also shows large variations with measurements ranging from 1.74 ± 0.04 mJy to 0.07 ± 0.01 mJy. The two other nights of our study (2019 April 19 and 2019 May 23) show less variation at the level of one to three magnitudes of change during the night. Figures 1 – 3 show the observed light curves. Figure 2. K ′ light curves of Sgr A* (black) and a comparison star, S0–17 (white, located about 02 from Sgr A*), on four nights of observations in 2019. We use stars within 1′′ of Sgr A* to characterize the photometric error at different Sgr A* brightness levels. The photometric uncertainties are typically less than 5% at high flux levels. Observations on 2019 May 13 also include H -band