If you want to take a more systematic approach then you could look at the ratios of intellectual to manual labour over time (they're not strict categories, but

If you want to take a more systematic approach then you could look at the ratios of intellectual to manual labour over time (they're not strict categories, but approximations would do) then you could also make an estimate of the rates at which both kinds of labour are being replaced by automation. In the limit everything turns into fixed capital, but that wouldn't work unless the machines themselves become independent economic actors and displace humans entirely.