Usually pretty darn close. If it is off by a minute either way just sight in at a longer distance. The first dial I got cut hit 5 inches high at 500 with a 100 yard zero. This was due to chronographing the loads at below 20 below and shooting them in our summer and Australia's winter. Sighting it in at 500 then slipping the dial to read 500 moved the error back so it was 1 inch low at 100 yards instead. That worked out fine, but dials are cheap and I ordered another one with the revised velocity. Korth cut that one for nothing when I explained what happened. In spite of that its nice to know how to tweak the system if you change bullets or loads a bit.