diff --git a/docs/research-data-sources b/docs/research-data-sources.md
similarity index 100%
rename from docs/research-data-sources
rename to docs/research-data-sources.md
diff --git a/src/argus/clients/exchangerate_client.py b/src/argus/clients/exchangerate_client.py
index 8ea5e89..1aa189e 100644
--- a/src/argus/clients/exchangerate_client.py
+++ b/src/argus/clients/exchangerate_client.py
@@ -1,12 +1,13 @@
-import requests as req
+import requests as reqs
 from argus.config import (
     EXCHANGE_RATE_BASE_URL,
     EXCHANGE_RATE_API_KEY,
     REQUEST_TIMEOUT_SECONDS,
 )
+from argus.domain.internal_models import MarketDataRequest
 
 
-def get_rates(curr1: str, curr2: str):
+def get_rates(req: MarketDataRequest) -> dict | None:
     """
     Get the exchange rate between two currencies using the ExchangeRate-API.
 
@@ -16,21 +17,23 @@ def get_rates(curr1: str, curr2: str):
 
     Returns: A dictionary containing the result status, error type (if any), and conversion rate (if successful).
     """
+    curr1 = req.instrument.base_currency
+    curr2 = req.instrument.quote_currency
     url = f"{EXCHANGE_RATE_BASE_URL}/{EXCHANGE_RATE_API_KEY}/pair/{curr1}/{curr2}"
     data = {"result": "", "error_type": "", "conversion_rate": None}
 
     try:
-        resp = req.get(url, timeout=REQUEST_TIMEOUT_SECONDS)
+        resp = reqs.get(url, timeout=REQUEST_TIMEOUT_SECONDS)
         resp.raise_for_status()
         payload = resp.json()
 
-    except req.exceptions.Timeout:
+    except reqs.exceptions.Timeout:
         print("API hat zu lange gebraucht.")
         return None
-    except req.exceptions.ConnectionError:
+    except reqs.exceptions.ConnectionError:
         print("Keine Verbindung zur API.")
         return None
-    except req.exceptions.RequestException as error:
+    except reqs.exceptions.RequestException as error:
         print(f"Request fehlgeschlagen: {error}")
         # Request fehlgeschlagen: 403 Client Error: Forbidden for url: https://v6.exchangerate-api.com/v6/None/pair/EUR/USD -> sollte nicht gezeigt werden!!!
         return None
diff --git a/src/argus/domain/validation.py b/src/argus/domain/validation.py
index 16879a7..1892f2c 100644
--- a/src/argus/domain/validation.py
+++ b/src/argus/domain/validation.py
@@ -211,3 +211,19 @@ def is_valid_op(op: str) -> bool:
     Return: bool - True if the operation is valid, otherwise False
     """
     return op in VALID_OPS
+
+
+def check_currency(question: str) -> str | None:
+    """
+    Checks if the input question contains a valid currency code.
+
+    Arg1: question: str - the question to be checked for a valid currency code
+
+    Return: str or None - the valid currency code if found, otherwise None
+    """
+    resp = normalize_input_string(question)
+
+    if is_valid_curr_code(resp):
+        return resp
+
+    return None
diff --git a/src/argus/gui/app.py b/src/argus/gui/app.py
index 02f4c1f..8009d7c 100644
--- a/src/argus/gui/app.py
+++ b/src/argus/gui/app.py
@@ -1,10 +1,14 @@
 import tkinter as tk
-import pandas as pd
+from datetime import date
 from matplotlib.backends.backend_tkagg import FigureCanvasTkAgg
-from argus.services.market_data_service import prepare_trend_analysis
-from argus.services.calculator_service import calc, check_op
-from argus.services.conversion_service import convert, check_currency
-from argus.domain.validation import parse_amount
+from matplotlib.figure import Figure
+from argus.services.trend_analysis_service import prepare_trend_analysis
+from legacy.services.calculator_service import calc, check_op
+from argus.services.market_data_service import convert
+from argus.domain.validation import parse_amount, check_currency
+from argus.domain.internal_models import DataSource, Instrument, MarketDataRequest
+
+db = ""
 
 
 def on_close() -> None:
@@ -69,7 +73,7 @@ def show_conv() -> None:
     conv_frame.pack(fill=tk.BOTH, expand=True)
 
 
-def show_trend() -> None:
+def show_trend(db: str) -> None:
     """
     Displays the trend chart in the application. It prepares the data for trend analysis,
     creates the trend chart, and updates the GUI to show the chart.
@@ -86,9 +90,17 @@ def show_trend() -> None:
     content.pack(side="top", fill=tk.BOTH, expand=True)
 
     if trend_canvas is None:
-        df = pd.DataFrame()
-        fig = prepare_trend_analysis(df)
-        if fig is None:
+        source = DataSource(name="", provider_kind="")
+        instrument = Instrument(symbol="EUR/USD", name="EUR - USD", asset_class="fx")
+        req = MarketDataRequest(
+            source=source,
+            instrument=instrument,
+            timeframe="1d",
+            start=date(2026, 1, 1),
+            end=date(2026, 1, 4),
+        )
+        fig = prepare_trend_analysis(db, req)
+        if not isinstance(fig, Figure):
             return None
         fig.set_size_inches(7, 4)
 
@@ -145,6 +157,21 @@ def act_convert() -> None:
     resp1 = check_currency(curr1.get())
     resp2 = check_currency(curr2.get())
     amount = parse_amount(amount_e.get())
+    source = DataSource(name="Exchange API", provider_kind="ex-api")
+    instrument = Instrument(
+        symbol="EUR/USD",
+        name="EUR - USD",
+        asset_class="fx",
+        base_currency=resp1,
+        quote_currency=resp2,
+    )
+    req = MarketDataRequest(
+        source=source,
+        instrument=instrument,
+        timeframe="1d",
+        start=date(2026, 1, 1),
+        end=date(2026, 1, 4),
+    )
 
     if resp1 is None:
         result_conv_label.config(text="Please enter a valid currency for 'Currency 1'")
@@ -160,7 +187,7 @@ def act_convert() -> None:
         )
         return
 
-    response = convert(amount, resp1, resp2)
+    response = convert(amount, req)
 
     if response is None:
         result_conv_label.config(text="Currency conversion error")
@@ -251,11 +278,15 @@ def app() -> None:
 # Buttons
 from_menu_calc = tk.Button(menu_frame, text="Calculator", command=show_calc)
 from_menu_conv = tk.Button(menu_frame, text="Converter", command=show_conv)
-from_menu_trend_chart = tk.Button(menu_frame, text="Trend Chart", command=show_trend)
+from_menu_trend_chart = tk.Button(
+    menu_frame, text="Trend Chart", command=lambda: show_trend(db)
+)
 
 from_sidebar_calc = tk.Button(sidebar, text="Calculator", command=show_calc)
 from_sidebar_conv = tk.Button(sidebar, text="Converter", command=show_conv)
-from_sidebar_trend_chart = tk.Button(sidebar, text="Trend Chart", command=show_trend)
+from_sidebar_trend_chart = tk.Button(
+    sidebar, text="Trend Chart", command=lambda: show_trend(db)
+)
 return_menu = tk.Button(sidebar, text="Back to menu", command=show_menu)
 
 click_calculate = tk.Button(calc_frame, text="Calculate", command=act_calculate)
diff --git a/src/argus/services/market_data_service.py b/src/argus/services/market_data_service.py
index 9328141..aae5bd1 100644
--- a/src/argus/services/market_data_service.py
+++ b/src/argus/services/market_data_service.py
@@ -1,5 +1,6 @@
 from argus.domain.internal_models import MarketDataRequest, MarketDataResponse
 from argus.clients.yfinance_client import get_timeseries
+from argus.clients.exchangerate_client import get_rates
 from argus.storage.database import read_price_bars, insert_price_bar
 import pandas as pd
 
@@ -45,3 +46,38 @@ def get_market_data(
             bars=pd.DataFrame(),
             message=str(e),
         )
+
+
+def get_conv_rate(req: MarketDataRequest) -> float | None:
+    """
+    Gets the conversion rate between two currencies.
+
+    Arg1: resp1: str - the first currency code
+    Arg2: resp2: str - the second currency code
+
+    Return: float or None - the conversion rate if found, otherwise None
+    """
+
+    data = get_rates(req)
+
+    if data is None:
+        return None
+
+    return float(data["conversion_rate"])
+
+
+def convert(amount: float, req: MarketDataRequest) -> float | None:
+    """
+    Converts an amount from one currency to another using the conversion rate.
+
+    Arg1: amount: float - the amount to be converted
+    Arg2: resp1: str - the first currency code
+    Arg3: resp2: str - the second currency code
+
+    Return: float or None - the converted amount if conversion rate is found, otherwise None
+    """
+
+    rate = get_conv_rate(req)
+    if rate is not None:
+        return amount * rate
+    return None
diff --git a/src/legacy/cli/interface.py b/src/legacy/cli/interface.py
index 727adaf..46401f2 100644
--- a/src/legacy/cli/interface.py
+++ b/src/legacy/cli/interface.py
@@ -1,5 +1,5 @@
-from argus.services.calculator_service import check_op, calc
-from argus.services.conversion_service import convert, check_currency
+from legacy.services.calculator_service import check_op, calc
+from legacy.services.conversion_service import convert, check_currency
 from argus.domain.validation import parse_amount
 
 
diff --git a/src/argus/services/calculator_service.py b/src/legacy/services/calculator_service.py
similarity index 100%
rename from src/argus/services/calculator_service.py
rename to src/legacy/services/calculator_service.py
diff --git a/src/argus/services/conversion_service.py b/src/legacy/services/conversion_service.py
similarity index 84%
rename from src/argus/services/conversion_service.py
rename to src/legacy/services/conversion_service.py
index 0dc3cf0..d4b2e0d 100644
--- a/src/argus/services/conversion_service.py
+++ b/src/legacy/services/conversion_service.py
@@ -1,4 +1,3 @@
-from argus.clients import exchangerate_client as ex_client
 from argus.domain.validation import normalize_input_string, is_valid_curr_code
 
 
@@ -18,7 +17,7 @@ def check_currency(question: str) -> str | None:
     return None
 
 
-def get_conv_rate(resp1: str, resp2: str) -> float | None:
+def get_conv_rate(resp1, resp2) -> float | None:
     """
     Gets the conversion rate between two currencies.
 
@@ -28,12 +27,12 @@ def get_conv_rate(resp1: str, resp2: str) -> float | None:
     Return: float or None - the conversion rate if found, otherwise None
     """
 
-    data = ex_client.get_rates(resp1, resp2)
+    # data = ex_client.get_rates(req)
 
-    if data is None:
+    if 0 == 0:
         return None
 
-    return float(data["conversion_rate"])
+    return None  # float(data["conversion_rate"])
 
 
 def convert(amount: float, resp1: str, resp2: str) -> float | None:
diff --git a/tests/test_exchangerate_client.py b/tests/test_exchangerate_client.py
index faf0864..e205439 100644
--- a/tests/test_exchangerate_client.py
+++ b/tests/test_exchangerate_client.py
@@ -1,39 +1,71 @@
 import requests as req
+import pytest
 from unittest.mock import Mock
+from datetime import date
+from argus.domain.internal_models import DataSource, Instrument, MarketDataRequest
 from argus.clients.exchangerate_client import get_rates, check_error
 
 
-def test_check_currency_timeout(monkeypatch):
+@pytest.fixture
+def sample_source():
+    return DataSource(
+        name="Exchange API", provider_kind="ex_client", requires_api_key=False
+    )
+
+
+@pytest.fixture
+def sample_instrument():
+    return Instrument(
+        symbol="EUR/USD",
+        name="EUR - USD Rate",
+        asset_class="fx",
+        base_currency="EUR",
+        quote_currency="USD",
+    )
+
+
+@pytest.fixture
+def sample_request(sample_source, sample_instrument):
+    return MarketDataRequest(
+        source=sample_source,
+        instrument=sample_instrument,
+        timeframe="",
+        start=date(2026, 1, 1),
+        end=date(2026, 1, 1),
+    )
+
+
+def test_check_currency_timeout(monkeypatch, sample_request):
     def test_get_resp(url, timeout):
         raise req.exceptions.Timeout()
 
     monkeypatch.setattr("requests.get", test_get_resp)
 
-    data = get_rates("EUR", "USD")
+    data = get_rates(sample_request)
     assert data is None
 
 
-def test_check_currency_connection_error(monkeypatch):
+def test_check_currency_connection_error(monkeypatch, sample_request):
     def test_get_resp(url, timeout):
         raise req.exceptions.ConnectionError()
 
     monkeypatch.setattr("requests.get", test_get_resp)
 
-    data = get_rates("EUR", "USD")
+    data = get_rates(sample_request)
     assert data is None
 
 
-def test_check_currency_request_exception(monkeypatch):
+def test_check_currency_request_exception(monkeypatch, sample_request):
     def test_get_resp(url, timeout):
         raise req.exceptions.RequestException("Testfehler")
 
     monkeypatch.setattr("requests.get", test_get_resp)
 
-    data = get_rates("EUR", "USD")
+    data = get_rates(sample_request)
     assert data is None
 
 
-def test_check_currency_value_error(monkeypatch):
+def test_check_currency_value_error(monkeypatch, sample_request):
     test_resp = Mock()
     test_resp.raise_for_status.return_value = None
     test_resp.json.side_effect = ValueError("Ungültige JSON-Antwort")
@@ -43,11 +75,11 @@ def test_get_resp(url, timeout):
 
     monkeypatch.setattr("requests.get", test_get_resp)
 
-    data = get_rates("EUR", "USD")
+    data = get_rates(sample_request)
     assert data is None
 
 
-def test_check_currency_key_error(monkeypatch):
+def test_check_currency_key_error(monkeypatch, sample_request):
     test_resp = Mock()
     test_resp.raise_for_status.return_value = None
     test_resp.json.return_value = {
@@ -61,11 +93,11 @@ def test_get_resp(url, timeout):
 
     monkeypatch.setattr("requests.get", test_get_resp)
 
-    data = get_rates("EUR", "USD")
+    data = get_rates(sample_request)
     assert data is None
 
 
-def test_check_currency_valid(monkeypatch):
+def test_check_currency_valid(monkeypatch, sample_request):
     test_resp = Mock()
     test_resp.raise_for_status.return_value = None
     test_resp.json.return_value = {
@@ -79,11 +111,11 @@ def test_get_resp(url, timeout):
 
     monkeypatch.setattr("requests.get", test_get_resp)
 
-    data = get_rates("EUR", "USD")
+    data = get_rates(sample_request)
     assert data == {"result": "success", "error_type": "", "conversion_rate": 1.2}
 
 
-def test_check_currency_invalid(monkeypatch):
+def test_check_currency_invalid(monkeypatch, sample_request):
     test_resp = Mock()
     test_resp.raise_for_status.return_value = None
     test_resp.json.return_value = {
@@ -97,7 +129,7 @@ def test_get_resp(url, timeout):
 
     monkeypatch.setattr("requests.get", test_get_resp)
 
-    data = get_rates("EUR", "USD")
+    data = get_rates(sample_request)
     assert data is None