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We propose to confirm the detection of the first isolated black hole (BH) comma OB110462. We analyzed archival HST data with improved astrometric techniques and demonstrate that the 3 sigma lower mass limit of OB110462 is 5 Msun comma making it a solid BH detection. However comma the allowed mass range of the BH is quite wide (68% CI of 9-31 Msun) comma due to the lack of sufficient time baseline of the archival data. We propose to obtain a new measurement of the target comma now 10 years after the lensing event comma in order to better constrain the baseline proper motion. This will allow the mass constraints of the BH to be improved by a factor of at least 2. This will provide the first mass measurement of an isolated BH comma which will inform theoretical models of massive star death comma the Milky Way BH mass distribution comma and the population of BH-BH binaries discovered via gravitational waves.