omron apr instruction

have a program that I have inherited that the instruction.

APR
D3570
D3501
D358

The value in D3570 is equal to 800 hex (+2048)
Could someone explain this instruction in simple terms?
I am tring to help a tech here in Dominican Republic and this instruction is just not making any sense to me at the moment.

THANKS

APR is a multi function instrustion - depends what the programmer has used it for. I commonly use it for linear approximation of a non linear curve. Are there any comments that may indicate how it is being used? Do you have a manual describing the functions?

For example, for linear approximation one would set up a table refernced in the instruction to say that eg the number count for 5ma input is 300, 6 ma is 472 ets and then the function will linearise the output. Particularly useful for cylindrical tanks on their side with belled ends.

By the way, Omron are the only PLCs I have used that have that function - there may be others but I have noy used any.