How do we compare/reconcile reported time-of-day during the 1860s with our present time measurement? During a presentation at the Chickamauga Battlefield the statement was made that "their" time was about 1 1/2 hours different than ours. Are there sources for an explanation of how officers measured time, set their watches, etc. and how that can be reconciled with our modern timekeeping? Almanacs? Sextants? Sundials?