function makeComputeErrorValue(type, value) {
    if(type === 'percent') {
        return function(dataPt) {
            return Math.abs(dataPt * value / 100);
        };
    }
    if(type === 'constant') {
        return function() {
            return Math.abs(value);
        };
    }
    if(type === 'sqrt') {
        return function(dataPt) {
            return Math.sqrt(Math.abs(dataPt));
        };
    }
}
Compute error bar magnitude (for all types except data)

@param {string} type error bar type
@param {numeric} value error bar value

@return {function} :
     @param {numeric} dataPt