Great product and great calculator.
My project (tiltable solar panel rack mounted on the side of a utility trailer) was pretty specialized so the calculator was the primary factor in deciding to go with this product. It is an awesome tool. But the underlying reasons for the relationship between the various measurements (A,B,C,D) is not intuitive, so required much experimentation with the configuration to get them within the required area. (Suggestions: I believe there is an error in the information balloon for "unused stroke". It says you cannot make the value less than 10mm - should be 10 inches. Also, it would be very helpful if "+" and "-" values could be assigned to the "C" value, as they are with the "B" values. When these values get small it is difficult to tell from the graph which side of the plane of the hinge they are located on.) The quality of the springs themselves is wonderful. I got the stainless steel ones and the fit and finish are first-class. Only complaint is that customer service interaction was somewhat cumbersome, with responses being limited to email, one question leading to another, etc. I read some reviews where apparently customers were able to call in, but no phone number is listed and I requested a phone call but never got one. I got to a good result but phone interaction would likely have saved considerable time.