Describing a still working self developed software system in a research paper. Which tense to use? Hello,

Ive developed a Software system, consisting of different parts for research purpose. And need to write a research thesis about this. Which will be my first scientific work in english ( iam not a native speaker, obviously).
However i'am not sure which tense i should use.

I developed the system for a research purpose(lets assume a red button which activates an alarm whenever someone is pushing it with a stress level than usual for this person, so the system needs to determine between usual and non usual stress level which is individual for every person)

After this step, i used this system in different setups and evaluated how the system performs in different setups ( IS the system able to track the higher stress level and activate the alarm. ( or do not acitvate the alarm if the stress level is usual for this person today [f.e. the person has a higher stress level the whole day, due to a fight with his girl friend in the morning, but the alarm should not ring as the persons stress level is higher than last week, but this level is usual for the todays condition])

Anyway, i know i should write the methodology part in simple present, because the experiment is finished whenever someone read this paper. ( the half of the participates watched a horror movie for 10 minute before they pressed the red button, while the other half watched the same movie for 1 minute before they pressed the button) 

But what is about the part in the methodology chapter where i describe the system? The system is still there Anyone could plug it in, and hit the red button, and the red button would scan for the heartbeat rate and send the information to the controlling unit, the controlling unit would do some math and if the value x is above 2 and the value y is above 12 the controlling unit would send a query to the server which would do some math and send back a value z. If the revived value z is above 2*(x+y) the controlling unit would activate the alarm.
the system is still working the same way as it worked when i did the experiments.

QUESTION:
Which tense should i use to describe the developed system in the methodology part?
Question: should I use anything other than the present indicative active tense to describe a system's behaviour. 

Question: is there any reason to write in another tense? Will it help a reader to understand the system better if they think of it as functioning at some time in the past? 

Answers: if you are describing a mis-behaving or erroneous system ("when I pressed button 'B' the system gave off a cloud of smoke") then it would be useful in that it would distinguish the mal-functioning instance. But you are trying to describe a properly-functioning system and so the present indicative active tense is preferable: "Press button B, The green light illuminates ...". It reads like a manual and so your write-up will be useful.