ATM you can buy 100x70mm 90 Degree Angle Corner Square Ruler for $13.99 (in Banggood). Price history, coupons and price alert are available on this page. What is best price?
Color: Silver, Material: Stainless Steel, Measurement Accuracy: DIN875-0 Grade, Size: 100x70mm
Latest coupon and price update (UTC):
Banggood ($13.99)
Banggood warehouse is located in China. So I have checked for active coupons (all category coupons and old ones), but there was no working coupon in Banggood. Is it cheap? Hmmm, price is higher than average (which is $11.99 right now), so better set price alert down below…
Link: Banggood product page
Price: $13.99
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): BGherra, BGBFCR32, BGsqus18, BGsqus20, BGbackwo, BG18baofu, BGDRB18, BG17331, BGb77dcc, BGWT15, BGa0b557, BGc8412f, BGWDT15
(there’s a little possibility that old coupon will work)
Aliexpress
There’re some similar (or not) items on Aliexpress
Click here to search by yourself. Here are coupons that you can use.
Price history and price alert
Here is price history (for all/most countries) for 100x70mm 90 Degree Angle Corner Square Ruler.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood and Aliexpress (only if product name will be the same as on Banggood and I will post it on social media though, so it’s more like Banggood price alert)).