There are two errors in your expression.
1. Multiplication signs "*" can't be omitted in OriginC's expressions. There are two signs missing in your formula.
2. Integer divided by an integer equals to an integer in OriginC. Therefore 1/440 will be zero. You should change it to 1.0/440 .
For example, you can change your formula as follows.
y = 1.0/( 1.0/b*( exp( b*a*(1.0/x - 1.0/440) )-1 ) + 1 );
You may check whether the two added signs are what you want.
Using initial values a = 100, b = 100 for fitting, you can get a good fitting result.
Sam
OriginLab Technical Services
