I'm trying to set up the correct wheel size for my Sigma 1009, on my wheel it has 26 x 2.35, but it does not have that size on the wheel size chart, what is the correct size.

I already referred you to Google and to Sigma support, but it sounds as if you probably need to replace the unit. It should work when you replace the battery, even if you have not set wheel size, as all bike computers come with a default setting. There is no way to "fix" such an inexpensive device (under $25 with shipping)
https://www.shop.com/Sigma+Topline+Wired+Bike+Computer+BC506+05160-1484064483-p+.xhtml?sourceid=298&CAWELAID=120179650032541809&CAGPSPN=pla&CAAGID=18133145218&CATCI=pla-152669075578&catargetid=120179650019543638&cadevice=c&gclid=Cj0KCQjw24nNBRChARIsALldLD0RZb-nYYKOoe52_lIzut84VQ406pw9AatsMu2TGjtjIT117rR1mx0aAoOwEALw_wcB

I’m happy to help further over the phone at https://www.6ya.com/expert/donald_f2ed37026a3ac881

Google "sigma bc 506 manual" or contact Signma:
SIGMA SPORT

I’m happy to help further over the phone at https://www.6ya.com/expert/donald_f2ed37026a3ac881

[PDF]Tire Circumference Chart - Cateye.pdf

www.cateye.com/data/resources/Tire_size_chart_ENG.pdf
CatEye47-559 26x1.75. 2023 202. 50-559 26x1.95. 2050 205. 54-559 26x2.10. 2068 207. 57-559 26x2.125. 2070 207. 58-559 26x2.35. 2083 208. ETRTO. Tire size. L.

Have you checked the manual? Pages 24 & 25 should be able to help you.
If you don't have a copy its available on the Sigma Sport site. http://www.sigmasport.com/en_media/produkte/bikecomputer/topline_2009/topline_wired/bc1609/allgemein/visuals/ba.pdf

If you really care about accuracy calculate it yourself (A) or roll it out, measure the distance (B) and set that according to the manual on the same page as the chart.

http://www.sigmasport.com/en/service_center/produkt_support/bikecomputer/

It's in the manual. Measure the wheel size and enter it manually.

http://www.sigmasport.com/en/allgemein/showdatei/?download=1&name=2_1_Manual_BC_1106_nat.pdf


There's a picture of how to determine the circumference by rolling the wheel one revolution and measuring it. Be as accurate as you can (to the mm).

4. Wheel size BIKE 1

• Press MODE to change to BIKE 1.

• Press SET briefly and the first digit flashes.

• Set the value by pressing RESET, change to the next digit by pressing MODE.
• Bike 1 is always the bike with the handlebar holder WS 1

All you need to do is measure the diameter and do the math or for precision, roll-out one revolution on the ground and measure it in millimeters and divide by 1.61 (or multiply times .621).

(Consult chart or figure yourself by measuring from the top of the tire to the ground in inches.) Measurement X 25.4 x 3.14 / 1.61 = ws ( / is divided by)

http://www.thisoldtractor.com/gtbender/mg_manuals/sigma_sport_bc1200.pdf

There's a chart in the link below. I believe Columns E and F apply.

http://www.sheldonbrown.com/cyclecomputer-calibration.html#ccc

get a tape measure and measure the out side circunfrance of the wheel. This is you number. OR put a white dob of paint on the tyre and roll it in a strainght line until the dob of paint makes a 2nd mark, (on a path way etc) measure the distance. this will be the same as the first option. Generally its required in mm.

700 x 25 = 2146


You should be all set :)

Push bottom button until you see TRIP in bottom left corner of screen. Then go to the back, and push the small button and hold for about 3 seconds. The WS in the top will be blinking, and the number will be blinking. Push the bottom button to scroll through until KMH is blinking. Then push the top button, to toggle to MPH. Now... you will have to rest your wheel size on this screen (the numbers) go to Sigma sports website and get the manual, then look at your wheel size on the side of the tire, put in the correct number for your wheel size. Once all this is done, then turn over and push the small button for about a second for your changes to take effect. the screen will not be blinking now.