Mill: Stacking Tolerances

I know my spindle has 0.0008" runout, so I marked the "high point" on the side of the spindle. In turn I've checked all my tooling and marked the "low point" on them. Then I always match up the marks when I mount the in the spindle, so the spindle's and tool's runout cancel each other out to some extent. For example, my ER25 collet chuck has 0.0005" runout (it's a cheap one from China), but when mounted in the spindle with the high and low points aligned I end up with with only 0.0003" runout total.