How to identify the cause of incorrect data in calculated item?

[BlackCrystal]

I have 2 items in zabbix version 5. first item as a trapper and it will be updated every one minute and Its value is ascending.
second item is calculated based on first item and its formula is : (abschange("KeyName"))/60

for example:
if values of first item are these: 5,8,16,34,68,71,93,102,...
then second item must return: 3,8,18,34,.. Then divide them by 60.

what i get is completely different. i checked in latest data and the first item is always correct and ascending but the second item seems that can't calculate absolute value.
how can i find the cause of this problem?

here is an example of what i get:
first item value: 148822441 ,148963574 ,149106618 ,149555694 ,...
second item value: 63498138, 2384, 63498138, 2384,...

i should mention that i had these exact items on zabbix 3 and they worked correctly. after migrating to zabbix 5 i face this problem.

[Hamardaban]

try use depended item, not calculated.
with preprocessing Arithmetic \ Custom multiplier 0,016667 or JS

[BlackCrystal]

would you please provide an example of how to turn this "(abschange("KeyName"))/60" into preprocessing step?

[Semiadmin]

Just create a dependent item with "change per second" in preprocessing

[Semiadmin]

You didn't write the exact version. In 5.4 functions and sintaxis very different from previous versions.

[BlackCrystal]

exact version is: 5.0.14

[Semiadmin]

Very strange, I don't know any difference in calculated items between 3.* and 5.0.

[Hamardaban]

Read how preprocessing works here https://www.zabbix.com/documentation.../preprocessing.
The dependent item gets the value of the parent item and converts it by preprocessing.

[BlackCrystal]

Thank you for your help. i could finally create the item that i wanted.