In some cases, we can expect to see small differences in the Atlas valuations and billing calculations. Like other performance management systems, Atlas is a trade based rather than a settlement based system. This means the billing valuations for accounts will always reflect the trade based value. This is one of the reasons that you can expect to see differences between Atlas valuations and custodial statement values.
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Atlas does not consume raw custodian statement valuations, but rather employs a complex portfolio accounting engine based on custodian reported transactions. Although this may seem counterintuitive this is why account valuations may not match the custodial statement exactly. In addition to trade vs settlement based accounting - accrued income payments or small rounding differences in security pricing could cause there to be slight differences in billing valuations.