Precision of apex DOS dosing problem.

[Tedca]

What is the precision of the DOS?
One of my channels doses KH, and during calibration it gives 39 ml instead of 40. I enter the result.
I currently dose 345 ml on that channel. DOS splits this into small doses of 4.4 ml, but when I check them they are only 4 ml.
I have the same problem with my Ca channel, which runs at a steady flow throughout the day of 2.4 ml, but when I measure it, it only gives 2 ml.
Are the doses too small?
Can it be calibrated against a smaller dose than the preset 40 ml?
Or is it possible to change the setting (via task, dosing) to dose fewer, larger doses?

 

[Rocks reef]

You should calibrate it before using it, yes.
They do ship with a factory set calibration, but it still needs to be done once setup for your tank.

 

[Tedca]

You should calibrate it before using it, yes.
They do ship with a factory set calibration, but it still needs to be done once setup for your tank.

I have calibrated it several times. Same result. The calibration is against 40ml but the adds for the 2-part is around 4ml every 15minute.
Am I the only one having this problem?
When crosschecked against calibration (same volume) the pump is spot on. It is when adding smal doses the accuracy drifts.