Before BBC BASIC (Z80) calculates trigonometric functions (`SIN`, `COS`, etc) of very large angles the angles are reduced to +/- PI radians. The larger the angle, the greater the inaccuracy of the reduction, and hence the result. When this inaccuracy becomes unacceptable, BBC BASIC (Z80) will issue an 'Accuracy lost' error message.

X=SIN(1E7)