Newbie seeks help with Astrology Chart consturction

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Hello Everyone,

I am new in this field and was wondering if anyone can help out with some problems i am having trying to construct these round orbital charts on my computer using a design software.

So I am trying to Track the Sun in the Tropical Zodiac so i can predict its postition exactly in a 360 degree chart at any date.
I start by normalizing to the start of the year , so that means that i make the start of a year eg.2017 0 degrees (in Cap) and the end (1st of Jan 2018 obviously in Cap) (360 degrees again or 0 degrees).

I take the Tropical geocentric solar cycle to be 365 , 5 hours 48 minutes etc etc....so i put that as the arc length total....Then when i want to find the position of the Sun at lets say x degrees from my 0 degrees in the zodiac i do simple Arc Length Maths and try to pin point the position of the Sun, however I am never exact keep missing by a day and a bit.

Eg. If my 0 degrees is 1st January 2017,....Today should be lets say around 43 degrees less than 2018 or 220 something from 2017.
THIS IS NEVER EXACT...I cant get it to work.
I am using values for the Sun in the tropical zodiac for today that i find on the internet.....Today 05 Sagitarious 32......(as all zodiacs are 30 degrees i add the 5 degrees and 32 minutes to the total arc degrees of the Sag Cusp from my starting point.

I am basically doing arc length maths using the positions of the sun in the tropical zodiac....but basic arc length maths dont seem to work...should they work?

What am I doing wrong anyone???
Thanks Muchly.