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Vernier Software and Technology
Vernier Software & Technology
Tech Info Library

How do LabQuest Curve fits work?

Labquest has five curve fit forms, whose coefficients are computed in one of two ways.

*** Linear form ***
Linear: y = mx +b

LabQuest uses the same approach as Logger Pro. See:
TIL 1869: How do we calculate linear fits in Logger Pro?

*** Non-linear forms ***
Proportional: y = Ax
Quadratic: y = Ax^2+Bx+C
Power: y = Ax^B
Natural Exponent: y = Aexp(-Cx)+B
Gaussian: y = A*e^(-(x-B)^2/(2*C^2))+D
Sine: y = A*sin(B*x+C)+D
Cosine: y = A*cos(B*x+C)+D
Cosine Squared: y = A*(cos(B*x+C))^2+D
Natural Logarithm: y = A*ln(B*x)

The coefficients of the non-linear forms are computed using the iterative, best-fit values approach of the Levenburg-Marquadt method. See http://en.wikipedia.org/wiki/Levenberg–Marquardt_algorithm

The root mean square error (RMSE) and uncertainties for each coefficient are also computed.

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We will be closed on August 21 to allow our employees to enjoy the Great American Eclipse.