4-20mA Scale for IFTTT is not Precise

[job-systems]

first item is when 0mA's value.
second item is when 20mA's value.

Hi @admin,

I tested what you say with signal generator and values are not coincident. 

Here the step by step of what I tested (I will put the picture number and an explanation at the side): 
01 = Configure ADC1
02 = Inside ADC1 I write unit in mA and put the same 0 to 20mA value of the analogue entrance. Press the button "SETTING" to save the configuration. 
03 = You can see on "Monitor" the values have been confirmed correctly. 
04 = I send 4.00 mA and I read 3.00 mA on webpage. 
05 = I send 12.00 mA and I read 10.45 mA on webpage. 
06 = I send 20.00 mA and I read 18.74 mA on webpage. 
07 = Configure ADC3.  Inside ADC3 I write unit in V and put the same 0 to 5V value of the analogue entrance.
08 = You can see on "Monitor" the values have been confirmed correctly. 
09 = I send 5.00 V and I read 5.00 V on webpage. Perfect. 
10 = I send 3.15 V and I read 3.13 V on webpage. Perfect. The difference is totally normal. 

Can you let me know if the test I did is correct?

Can you help me solve this problem so scale is coincident with what we read?

Thank you.